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{{Short description|none}}
This is a list of the '''evolution of the ]s of the ]'''. It lists each change to the internal and external borders of the country.
{{Redirect|Westward expansion|trails in the American Old West|Westward Expansion Trails}}
]
]
] came under control of the United States.<ref>{{cite news |title=History of the Northern Mariana Islands |url=https://www.britannica.com/place/Northern-Mariana-Islands/German-and-Japanese-control |work=Encyclopædia Britannica}}</ref>]]
The ] was formed after ] in North America ] from the ] on July 4, 1776. In the ], passed by the ] two days prior, the colonies resolved that they were free and independent states. The union was formalized in the ], which ] on March 1, 1781, after being ratified by all 13 states. Their independence was recognized by ] in the ] of 1783, which concluded the ]. This effectively doubled the size of the colonies, now able to stretch west past the ] to the ]. This land was organized into territories and then states, though there remained some conflict with the sea-to-sea grants claimed by some of the original colonies. In time, these grants were ] to the federal government.


The first great expansion of the country came with the ] of 1803, which doubled the country's territory, although the southeastern border with ] was the subject of much dispute until it and Spanish claims to the ] were ceded to the US in 1821. The Oregon Country gave the United States access to the ], though it was shared for a time with the ].<ref name="vz-1818"/> The annexation of the ] in 1845 led directly to the ], after which the victorious United States obtained the northern half of ]'s territory, including what was quickly made the state of ].<ref name="vz-ca"/>
==Notes==
*This list does not include ], such as ], ], and the ].
*"]" is not a name; it simply means that this territory has not had an ] passed. In most situations, the purpose of unorganized territory was to act as land for ] settlement. Later, the last unorganized territory in the country was indeed referred to as "]", though this is not an official name.
*Dotted lines on the borders mean that region is part of a country not fully shown on the map, since it's confined to the present-day borders of the United States. An exception is ], which extended beyond the area of the map.
*Many territorial disputes and borders from early in the United States' history are unclear. For example, the border between ] and ] seems unclear. For the purposes of simplicity, this article uses the original border, the ], even though later maps tended to move it west to the ]. This is partly because the Organic Act for Florida specified that it included parts of both West and East Florida; if the border were the Perdido River, then Florida Territory would not have included any of West Florida, it having already been divided among Louisiana, Mississippi, and Alabama.{{fact}}
*Several very small changes are not included in these maps:
#The retrocession of land back to ] by the ]
#The resolution of the ] in ]
#The transfer of the ] from ] to the federal government, then to ]
#The transfer of the ] from ] to ]
#Various ] with ].
#The ], since it arose from a total lack of surveying, rather than a dispute over the surveyed lines; it would also appear quite small on the map.
#The dispute over ], a square mile of land claimed by ] and ].
#When ] was created, it also included land south of 43° N and north of the ] and ] rivers. This land was not part of ] when it became a state, and was transferred to Nebraska in ].


As the development of the country moved west, however, the question of ] became more important, with vigorous debate over whether the new territories would allow slavery and events such as the ] and ]. This came to a head in 1860 and 1861, when the governments of the ] proclaimed their secession from the country and formed the ]. The ] led to the defeat of the Confederacy in 1865 and the eventual readmission of the states to the ]. The cultural endeavor and pursuit of ] provided a strong impetus for westward expansion in the 19th century.
==1780s-1790s==
]
;] ]
The ] came in to effect, forming the new nation. Note that the states ratified at different times, but to simplify the map, the final result is shown here.


The United States began expanding beyond North America in 1856 with the passage of the ], causing many small and uninhabited, but economically important, islands in the ] and the Pacific Ocean to be claimed.<ref name="guano"/> Most of these claims were eventually abandoned, largely because of competing claims from other countries. The Pacific expansion culminated in the ] in 1898, after the ] of its government five years previously. ], the last major acquisition in North America, was ] from ] in 1867. Support for the ] from the ], and the sinking of the ], led to the ] in 1898, in which the United States gained ], ], and the ], and occupied Cuba for several years. ] was acquired by the United States in 1900 after the end of the ].<ref>Ryden, George Herbert. ''The Foreign Policy of the United States in Relation to Samoa''. New York: Octagon Books, 1975.</ref> The United States ] from Denmark in 1917.<ref>http://www.vinow.com/general_usvi/history/ Vinow.com. Virgin Islands History. Retrieved January 18, 2018.</ref> Puerto Rico and Guam remain territories, and the Philippines became independent in 1946, after being a major theater of ].
Some peculiarities to point out to those familiar only with the current borders: Many states had ]s from the British crown that they would not give up easily, so they ] to the federal government in exchange for their ] debts. However, ] did not do so until much later; ] ceded most land but kept its ]; Virginia ceded its claim to the territory north and west of the ]; and North Carolina ceded its claim to its western counties. The last two are shown on this map as ].


Following the war, ] were ] to the U.S. by the ],<ref name="ttpi"/> and while the ] became a U.S. territory, the ], ], and ] emerged from the trust territory as independent nations. The last major international change was the acquisition in 1904, and return to ] in 1979, of the ], an unincorporated US territory which controlled the ]. The final cession of formal control over the region was made to Panama in 1999.
] claimed a border further north than what the United States said it had. Its border had been 31&deg; north when Spain ceded it to the ]. The British later moved its border north to 32&deg;38' latitude, but when it was ceded back to ] in the ], the British cited the original border at the 31st parallel, but Spain continued to claim the higher border. Also, the borders at the northern area of the ] of ] and the area northwest of ] remained disputed.
{{-}}


States have generally retained their initial borders once established. Only three states (], ], and ]) have been created directly from area belonging to another state (although at the time of admission, Vermont agreed to a monetary payment for New York to relinquish its claim); all of the other states were created from federal territories or from acquisitions. Four states (], ], ], and ]) have expanded substantially by acquiring additional federal territory after their initial ]. In 1912, ] was the last state established in the ], commonly called the "lower 48". In 1959, ] was the 50th and most recent state admitted.
]
;] ]
The unorganized lands were organized into the Territory North West of the ], or ], and the Territory South West of the Ohio River, or ].
{{-}}


==Legend for maps==
]
::::'''Key to map colors'''
;] ]
::::{{legend|#FFFFE0|United States states (domestic maps), undisputed area of United States (dispute maps)}}
The ] was admitted as the 14th state, ].
::::{{legend|#FFDEAD|United States territories (domestic maps)}}
{{-}}
::::{{legend|#D76767|disputed area of United States}}
::::{{legend|#c0c09c|area changed by event}}


==1776–1784 (American Revolution)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
The ] was formed from land granted by ] and ]; the Virginia portion would later be returned.
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|July 4, 1776
|] of the ] in North America collectively ] as the United States of America,{{efn|The borders of the country followed the colonial borders; for simplicity, the maps use the borders defined in the 1783 ]. The only substantive difference between the borders before and after the Treaty of Paris is the southwest border: when Great Britain had ownership over West Florida, they had moved its border north, to a line east from the mouth of the ], and that area thus did not belong to Georgia; the treaty granted the area between this and ] to the United States.}} though several colonies had already individually declared independence:<ref name="declaration">{{cite web |url=https://www.archives.gov/founding-docs/declaration-transcript |title=Declaration of Independence: A Transcription |date=November 2015 |publisher=] |access-date=September 7, 2017}}</ref>
* The ], becoming the ]<ref name="vz-ct">Van Zandt, pp. 72–74</ref>
* The ], commonly known as the Lower Counties on Delaware, which was ] before their declaration of independence on June 15, 1776<ref name="vz-de">Van Zandt, pp. 84–85</ref><ref>{{cite web|url=http://delaware.gov/topics/facts/gov.shtml |title=Delaware Government Facts & Symbols |publisher=Government of Delaware |access-date=January 16, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170109144723/https://delaware.gov/topics/facts/gov.shtml |archive-date=January 9, 2017 }}</ref>
* The ], becoming the ]<ref name="vz-ga">Van Zandt, pp. 100–104</ref>
* The ], becoming the ]<ref name="vz-md">Van Zandt, pp. 85–88</ref>
* The ], becoming the ]<ref name="vz-ma">Van Zandt, pp. 65–71</ref>
* The ], which was the ] before their declaration of independence on June 15, 1776<ref name="vz-nh">Van Zandt, pp. 60–64</ref><ref>{{cite book |url=https://books.google.com/books?id=AYk0AQAAMAAJ |title=The Laws of the State of New Hampshire |year=1824 |pages=239–240 |access-date=January 16, 2017|last1=Hampshire |first1=New }}</ref>
* The ], becoming the ]<ref name="vz-nj">Van Zandt, pp. 79–80</ref>
* The ], becoming the ]<ref name="vz-ny">Van Zandt, pp. 74–79</ref>
* The ], becoming the ];<ref name="vz-nc">Van Zandt, pp. 96–99</ref> some believe the colony ] on May 20, 1775, but this is disputed
* The ], becoming the ]<ref name="vz-pa">Van Zandt, pp. 80–84</ref>
* The ], commonly known as Rhode Island, which was the ] before declaring independence on May 4, 1776<ref name="vz-ri">Van Zandt, pp. 71–72</ref><ref>{{cite web|url=http://www.history.com/this-day-in-history/rhode-island-declares-independence |title=Rhode Island declares independence |publisher=] |access-date=January 16, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170118033158/http://www.history.com/this-day-in-history/rhode-island-declares-independence |archive-date=January 18, 2017 }}</ref>
* The ], becoming the ]<ref name="vz-sc">Van Zandt, pp. 99–100</ref>
* The ], becoming the ]<ref name="vz-va">Van Zandt, pp. 92–95</ref>


The capital was not specifically established; at the time, the ] met in ].<ref name="capitals">{{cite web|url=https://www.senate.gov/reference/reference_item/Nine_Capitals_of_the_United_States.htm |title=Nine Capitals of the United States |publisher=U.S. Senate |access-date=March 19, 2016 |archive-url=https://web.archive.org/web/20160320084755/https://www.senate.gov/reference/reference_item/Nine_Capitals_of_the_United_States.htm |archive-date=March 20, 2016 }}</ref><ref name="histcaps">{{cite web|url=http://www.history.com/news/8-forgotten-capitals-of-the-united-states |title=8 Forgotten Capitals of the United States |publisher=] |access-date=March 12, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170126151622/http://www.history.com/news/8-forgotten-capitals-of-the-united-states |archive-date=January 26, 2017 }}</ref>
]
;] ]
The western counties of ] were split and quickly admitted as the 15th state, ].
{{-}}


Many states had vaguely defined and surveyed borders; these are not noted as contested in the maps unless there was an active dispute. The borders of North Carolina were particularly poorly surveyed, its border with South Carolina having been done in several pieces, none of which truly matched the spirit of the charter,<ref>{{cite web|url=http://www.carolana.com/Carolina/Noteworthy_Events/NC_SC_border_surveys.html |title=The North Carolina – South Carolina Border Surveys – 1730 to 1815 |access-date=December 30, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160304054336/http://www.carolana.com/Carolina/Noteworthy_Events/NC_SC_border_surveys.html |archive-date=March 4, 2016 }}</ref><ref>{{cite news|url=https://www.nytimes.com/2014/08/24/opinion/sunday/how-the-carolinas-fixed-their-blurred-lines.html?_r=0 |title=How the Carolinas Fixed Their Blurred Lines |work=] |author=Kelly, Stephen R. |date=August 23, 2014|access-date=December 30, 2015 |url-status=live |archive-url=https://web.archive.org/web/20140831014105/http://www.nytimes.com/2014/08/24/opinion/sunday/how-the-carolinas-fixed-their-blurred-lines.html?_r=0 |archive-date=August 31, 2014 }}</ref> and its border with Virginia was only surveyed roughly halfway inland from the sea.
]
;] ]
], also known as the Treaty of San Lorenzo, settles the northern border of ] as the 31st parallel.
{{-}}


Several northeastern states had overlapping claims: Connecticut, Massachusetts Bay, and New York all claimed land west of their accepted borders, overlapping with each other and with a sizable claim by Virginia. Of the three, only Connecticut seriously pursued its claims, while Virginia is considered to have had the most legitimate claim to the vast northwest, dividing it into counties and maintaining some limited control.
]
;] ]
The ] was admitted as the 16th state, ].
{{-}}


The entirety of the new United States was claimed by Great Britain, including ] and ], two small islands off the northeast coast which remain disputed up to the present.<ref>{{cite news | url=https://nationalpost.com/news/canada/a-haven-for-puffins-tranquil-island-off-nova-scotia-is-a-rare-piece-of-disputed-territory-between-canada-and-the-u-s | title=Puffin Wars: The island paradise at centre of last Canada-U.S. land dispute | newspaper=] | author=O'Connor, Joe | date=November 27, 2012 | access-date=April 1, 2019}}</ref>
]
|align="center"|]<br /><br />Disputes:<br />
;] ]
]
Due to the ], an act was signed by ] ], authorizing him to appoint commissioners to negotiate with ] about ceding its ], and created ] in the region ceded by West Florida.<ref></ref>
|-
{{-}}
!scope=row|September 20, 1776
|The Counties of New Castle, Kent, and Sussex, upon Delaware enacted a ], renaming itself ].<ref>{{cite web|url=http://avalon.law.yale.edu/18th_century/de02.asp |title=Constitution of Delaware |year=1776 |publisher=] |work=] |access-date=June 10, 2009 |url-status=live |archive-url=https://web.archive.org/web/20090709205617/http://avalon.law.yale.edu/18th_century/de02.asp |archive-date=July 9, 2009 }}</ref>
|align="center"|]
|-
!scope=row|September 28, 1776
|The State of Pennsylvania enacted a ], renaming itself the ].<ref>{{cite web|url=http://avalon.law.yale.edu/18th_century/pa08.asp |title=Constitution of Pennsylvania |year=1776 |publisher=] |work=] |access-date=January 16, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170126144236/http://avalon.law.yale.edu/18th_century/pa08.asp |archive-date=January 26, 2017 }}</ref>
|align="center"|''no change to map''
|-
!scope=row|December 20, 1776
|To avoid ] forces who were advancing on ], the ] began meeting in ].<ref name="capitals"/><ref name="histcaps"/>
|align="center"|]
|-
!scope=row|January 15, 1777
|The northeastern region of ], known as the ], declared independence as ].<ref name="vz-vt"/><ref>{{cite book | url=https://archive.org/details/provincialandst01courgoog | title=Provincial and State Papers relating to New Hampshire | year=1877 | access-date=January 16, 2017 | pages=–246| last1=Court | first1=New Hampshire (Colony) Probate }}</ref><ref name="newconnecticut">Vermont 2006 J.R.H. 3, {{webarchive|url=https://web.archive.org/web/20061011144319/http://www.leg.state.vt.us/docs/legdoc.cfm?URL=%2Fdocs%2F2006%2Facts%2FACTR105.HTM |date=October 11, 2006 }}</ref>
|align="center"|Disputes:<br />
]
|-
!scope=row|March 4, 1777
|The ] returned to ] after the threat to it by ] forces ended.<ref name="capitals"/><ref name="histcaps"/>
|align="center"|]
|-
!scope=row|June 4, 1777
|New Connecticut was renamed ].<ref name="newconnecticut"/><ref name="vz-vt"/>
|align="center"|Disputes:<br />
]
|-
!scope=row|September 27, 1777
|The ] fled ] after the American defeat at the ], and briefly met in ]<ref name="capitals"/><ref name="histcaps"/>
|align="center"|]
|-
!scope=row|September 30, 1777
|The ] continued to move away from ], settling in ].<ref name="capitals"/><ref name="histcaps"/>
|align="center"|]
|-
!scope=row|June 11, 1778
|] claimed what was called the "East Union", consisting of some towns in ] that petitioned on March 12, 1778, to join with Vermont, out of concern that their state was focusing too much on its coastal region. Vermont never gained full control over the area.<ref name="vz-vt"/><ref name="vt-firsteastunion">, pp. 89–103</ref><ref name="vt-unions"/><ref name="vt-enc-east-union"/>{{efn|The New Hampshire towns petitioning to join Vermont were: ] (now Littleton), ], ], ] (now Orange), ], ] (now part of Hanover), ], ], ] (now Lisbon), ], ], ], ], ], ], and ].<ref name="vt-firsteastunion"/> The specific extent of the towns annexed is unknown, as township borders were often delineated only when a dispute arose; the map uses the common interpretation.}}
|align="center"|Disputes:<br />]
|-
!scope=row|October 21, 1778
|Under pressure from the ], ] rescinded the annexation of the East Union; the legislature declared on February 12, 1779, that the East Union should be considered null from its beginning.<ref name="vt-firsteastunion"/><ref name="vt-unions"/><ref name="vt-enc-east-union"/>
|align="center"|Disputes:<br />]
|-
!scope=row|July 2, 1779
|The ] returned to ] following ] ].<ref name="capitals"/><ref name="histcaps"/>
|align="center"|]
|-
!scope=row|August 31, 1779
|] surrendered its ] to southwest ].<ref name="vz-pa"/><ref>{{cite journal|last=Crumrine|first=Boyd|date=1902|title=Boundary Controversy between Pennsylvania and Virginia; 1748–1785|url=https://archive.org/details/boundarycontrove00crum|journal=]|volume=1|issue=4 |pages=505–568|doi=10.5962/p.331066 |s2cid=251488742 |access-date=August 20, 2017|doi-access=free}}</ref>
|align="center"|]
|-
!scope=row|March 23, 1780
|] and ] surveyed their border further inland. Virginia's survey reached the ] on this date,<ref>{{Cite book |last=Hening |first=William Waller |url=https://archive.org/details/statutesatlargeb09virg/page/564/mode/2up |title=The statutes at large; being a collection of all the Laws of Virginia |last2=Virginia (Colony) Laws |first2=statutes |last3=Hening |first3=William Waller |date=1809 |volume=9 |page=564}}</ref> while North Carolina's team stopped at the ] and filed their survey on November 17, 1779.<ref>{{Cite journal |last=Hardin |first=Bayless E. |date=1946 |title=The Kentucky Boundary |url=https://www.jstor.org/stable/23372488 |journal=Register of Kentucky State Historical Society |volume=44 |issue=146 |page=11 |issn=2328-8183}}</ref> The two surveys were roughly two miles apart, creating a thin area claimed by both states. While the border was intended to follow ], early surveying errors caused it to veer north of that, reaching a distance of almost ten miles off by the time it reached the Tennessee River.<ref name='tn-va-border'>{{cite web|url=http://www.virginiaplaces.org/boundaries/tnboundary.html |title=Virginia-Tennessee Border |access-date=August 30, 2023 |url-status=live |archive-url=https://web.archive.org/web/20230801064052/http://virginiaplaces.org/boundaries/tnboundary.html |archive-date=August 1, 2023 }}</ref><ref name="vz-va"/>
|align="center"|]
|-
!scope=row|October 25, 1780
|The State of Massachusetts Bay enacted a ], renaming itself the ].
|align="center"|]
|-
!scope=row|March 1, 1781
|The ] entered into force.<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/artconf.asp
|title=Articles of Confederation
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151029080610/http://avalon.law.yale.edu/18th_century/artconf.asp
|archive-date=October 29, 2015
}}</ref>
|align="center"|''no change to map''
|-
!scope=row|April 4, 1781
|] again claimed an East Union, consisting of some towns in ] that wished to join with Vermont; more towns were interested than during the first attempt in 1778, though again, the exact extent of the borders is unknown. Vermont never gained full control over the area.<ref name="vz-vt"/><ref name="vt-state-papers-136-137">, pp. 136–137: "Agreeably to the recommendation of the committees, the Legislature of Vermont was adjourned to the first Wednesday of April ; at which time, it met at Windsor, and the union of the grants, east and west of Connecticut river, was consummated"</ref><ref name="vt-unions">{{cite web|url=http://academics.smcvt.edu/vtgeographic/textbook/historical/historical_geography_of_vermont.htm |title=The Historical Geography of Vermont |access-date=January 24, 2016 |archive-url=https://web.archive.org/web/20160112223456/http://academics.smcvt.edu/vtgeographic/textbook/historical/historical_geography_of_vermont.htm |archive-date=January 12, 2016 }}</ref><ref name="vt-enc-east-union">{{cite encyclopedia | encyclopedia=The Vermont Encyclopedia | title=East Union | year=2003 | publisher=University Press of New England | id=1584650869 | url=https://books.google.com/books?id=uTBCXqOou0YC&pg=PA111 | page=111| isbn=978-1-58465-086-7 }}</ref>{{efn|The New Hampshire towns petitioning to join Vermont were: ], ], ], ] (now Orange), ], ], ], ], ], ], ], ], "Gilsom" (likely ]), ], ], ] (now Lisbon), ], ], ], ], ], ], "Leinster" (possibly ]), ], ], ], ], ], ], ], ], ] (now Sunapee), ], ], and ].<ref name="vt-state-papers-136-137"/> The specific extent of the towns annexed is unknown, as township borders were often delineated only when a dispute arose; the map uses the common interpretation.}}
|align="center"|Disputes:<br />]
|-
!scope=row|June 16, 1781
|] claimed what was called the "West Union", consisting of some towns in ], mainly to counterbalance Vermont's attempt at eastward expansion. Vermont never gained full control over the area.<ref name="vz-vt"/><ref name="vt-unions"/><ref name="vt-state-papers-138">, pp. 138–141</ref><ref name="vt-enc-west-union">{{cite encyclopedia | encyclopedia=The Vermont Encyclopedia | title=West Union | year=2003 | publisher=University Press of New England | id=1584650869 | url=https://books.google.com/books?id=uTBCXqOou0YC&pg=PA319 | page=319| isbn=978-1-58465-086-7 }}</ref> The specific date this occurred is unclear; sources suggest June 16, June 26, and July 18.{{efn|The New York towns petitioning to join Vermont were: "Black-Creek" (unknown; possibly is or is near ]), ], ], ], "Greenfield" (unknown; there is a town named ] but it lies west of the ], which was explicitly the western extent of the West Union), ], ], "Little Hoosack" (unknown; presumably near Hoosick), ], "Scorticook" (possibly ]), ] (now Whitehall), and "Upper-White-Creek" (probably ]).<ref name="vt-state-papers-138"/> The specific extent of the towns annexed is unknown, as township borders were often delineated only when a dispute arose; the map uses the common interpretation.}}
|align="center"|Disputes:<br />]
|-
!scope=row|February 22, 1782
|] abandoned its attempts to annex the East Union from ] and the West Union from ].<ref name="vz-vt"/><ref name="vt-enc-east-union"/><ref name="vt-enc-west-union"/><ref name="ReferenceA">{{ussc|name=Vermont v. New Hampshire|volume=289|page=593|year=1933}}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|October 29, 1782
|The federal government accepted the ] from ] of its western claims, which the state ceded on February 19, 1780, and executed on March 1, 1781; New York proclaimed its new western border to be a line drawn south from the western end of ]. At its maximum interpretation, the state had claimed an area bounded by ], ] and ]; to the ], ], and ] Rivers; and north along the ], ending at the border with ].<ref name="walker-cessions">Walker, section titled "Areas and Political Divisons of the United States", p. 1 (p. 64 of the entire book)</ref> It is unclear from where this claim came; many sources state that New York had surrendered it, but very few elaborate on how it was obtained. One source states that it was a cession by the ], who had conquered much of the region.<ref>{{cite web|url=http://www.virginiaplaces.org/boundaries/cessions.html |title=Virginia's Cession of the Northwest Territory |access-date=June 21, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160817091436/http://www.virginiaplaces.org/boundaries/cessions.html |archive-date=August 17, 2016 }}</ref> However, New York never seriously enforced these claims. The cession included the small tip of New York north of Pennsylvania, which came to be known as the ].<ref>{{cite book | url=https://books.google.com/books?id=yIwMAQAAMAAJ&pg=PA384 | title=The United States: its beginnings, progress and modern development, Volume 3 | author=Spencer, Jesse Ames | access-date=January 14, 2016| year=1912 }}</ref><ref name="vz-ny"/>
|]
|-
!scope=row|December 30, 1782
|The ] declared that the land that ] claimed in northern ] was part of Pennsylvania, thus attempting to end the ].<ref>{{cite journal | journal=Proceedings of the New Jersey Historical Society | volume=6 | year=1921 | title=The "Pennamite Wars" and the Trenton Decree of 1782 | author=Gnichtel, Frederick W. | url=https://books.google.com/books?id=k7WfAAAAMAAJ&pg=PA31 | access-date=November 8, 2015}}</ref><ref name="vz-pa"/> The claim was an extension of Connecticut's northernmost and southernmost borders westward, skipping ] and ], though as Connecticut's northern border was a few miles north of ]'s northern border, a small sliver of New York was also claimed. While conflict would continue for some time, this was the end of the formal claim by Connecticut.
|]
|-
!scope=row|June 30, 1783
|The ], and the ] government reaction to it, caused the ] to leave ] for ].<ref name="capitals"/>
|align="center"|]
|-
!scope=row|November 26, 1783
|The ] reconvened in ].<ref name="capitals"/>
|align="center"|]
|-
!scope=row|March 1, 1784
|] ceded ] northwest of the ] to the federal government.<ref>{{cite book|title=Journals of the Continental Congress, 1774–1789|pages=Vol. 26, pp. 112–121|url=http://memory.loc.gov/cgi-bin/ampage?collId=lljc&fileName=026/lljc026.db&recNum=117&itemLink=r%3Fammem%2Fhlaw%3A%40field%28DOCID%2B%40lit%28jc0261%29%29%230260001&linkText=1|editor=Worthing C. Ford|display-editors=etal}}</ref><ref name="vz-va"/> ] continued to claim its western lands that had overlapped with Virginia's cession.
|]
|-
!scope=row|May 12, 1784
|] ] the independence of the United States, ending its claim to the country.<ref name="vz-boundaries">Van Zandt, pp.10–22</ref><ref name="treatyofparis">; International Treaties and Related Records, 1778–1974; General Records of the United States Government, Record Group 11; National Archives.</ref>{{efn|The treaty established the boundaries of the new country, from the ]: up the "St. Croix River" (which river this referred to was disputed) to its source; north to the height of the land (the "Northwest Angle of Nova Scotia"); along the height of the land to the "northwesternmost Head" of the ] (which source this referred to was disputed); down that to ]; west to the ]; up that to the ], through ], the ], ], the ], ], the ], ], and ]; to "Long Lake" (which lake this referred to was disputed) towards the ]; to the northwest angle of the Lake of the Woods; then west to the ]. However, the Lake of the Woods was north of the source of the Mississippi River; maps universally show this undefined border as a straight line, nearly straight south, between the two points. From there, it followed the Mississippi River down to ]; east to the ]; down that to the confluence of the Chattahoochee and ] rivers; a line from there to the source of the ]; then down that to the ].<ref name="treatyofparis"/>}} The treaty ended the ], though military action had largely ended after the ] victory at ] on October 19, 1781.


Because of ambiguities and poor knowledge of geography, the treaty was unclear in several areas:
==1800s==
* The northeastern border was defined as running from the headlands of the ], but there were several options for that.
]
* The northwestern border was defined as a line running west from the ] to the ], but the river's source was south of that; maps universally show the line as running directly from the ] to the river's source, ].
;] ]
* The border extending from ] towards the Lake of the Woods was poorly defined as starting from "Long Lake", which both sides interpreted to their advantage.
] was formed from the western portion of ].
* ] and ] off the northeast coast remained disputed, as did ] off the ].
{{-}}


The ] also involved treaties with ] and ], with Great Britain ceding the ] to ]. During their ownership of ], the British had moved its border north, and the cession to Spain appeared to apply to the full extent of the British colony. However, the British-American treaty granted the extension of West Florida to the United States, where it enlarged ] south to ], indicating that only the original definition of West Florida was to be ceded to Spain. The local Spanish governors also made a move to occupy forts along the ], with claims to everything south of the ]; it is unknown how official or strong these claims were, and they are not mapped as they are in conflict with the other Spanish claim involving the border of West Florida.<ref>{{cite book | url=https://archive.org/details/historyoftenness00mcgerich | title=A History of Tennessee from 1663 to 1914: For Use in Schools | publisher=American Book Company | author=McGee, Gentry Richard | pages=–99 | access-date=December 29, 2015| year=1911 }}</ref>
]
|align="center"|]<br /><br />Disputes:<br />]
;] ]
|}
] ceded its ] to the federal government, which made it part of ].
{{-}}


==1784–1803 (Organization of territory)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
] finally ceded its western claims, the ], to the federal government, where it became unorganized land. Also, on ] ], the ] transferred the ] from ] to ].
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|August 23, 1784
|A region in central ] (modern-day eastern ]), unhappy with the state's governance over the area, declared independence from the state as the ].{{efn|There is disagreement over if the state was named Franklin or Frankland; sources tend to refer to Franklin as the specific state, and Frankland as the region.<ref>{{Cite journal |last=McGill |first=J. T. |date=1925 |title=Franklin and Frankland: Names and Boundaries |url=https://www.jstor.org/stable/42637503 |journal=Tennessee Historical Magazine |volume=8 |issue=4 |pages=248–257 |issn=2333-9012}}</ref>}}<ref>{{cite book | title=History of the Lost State of Franklin | author=Williams, Samuel C. | year=1933 | url=https://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/America/United_States/_Topics/history/_Texts/WILLSF/home.html | page=30}}</ref><ref>{{Cite journal |last=Alden |first=George Henry |date=1903 |title=The State of Franklin |url=https://www.jstor.org/stable/1832926 |journal=The American Historical Review |volume=8 |issue=2 |pages=271–289 |doi=10.2307/1832926 |issn=0002-8762}}</ref> The government of Franklin held some control over the area, and petitioned for statehood, receiving support from seven of the nine states required, but would only last a few years.<ref name="franklin">{{cite news|url=http://www.bnd.com/living/liv-columns-blogs/answer-man/article100650397.html |title=The state that almost was an original colony |work=Belleville News-Democrat |access-date=March 13, 2017 |date=September 8, 2016 |author=Schlueter, Roger |url-status=live |archive-url=https://web.archive.org/web/20160909150837/http://www.bnd.com/living/liv-columns-blogs/answer-man/article100650397.html |archive-date=September 9, 2016 }}</ref><ref name="vz-tn"/>
|align="center"|Unofficial change:<br />]
|-
!scope=row|November 1, 1784
|The ] moved for a short time to ].<ref name="capitals"/>
|align="center"|]
|-
!scope=row|January 11, 1785
|The ] moved to ], and would settle there for five years.<ref name="capitals"/>
|align="center"|]
|-
!scope=row|April 19, 1785
|The federal government accepted the ] from ] of its extreme western claim, which was never seriously enforced.{{efn|Massachusetts's ceded claim was a strip of land west of ] and ] stretching to the ], bounded by the latitudes of ]'s original charter: on the north by a line west from one league north of ], and on the south by a line west from Massachusetts' southwest corner.<ref name="walker-cessions"/>}}<ref name="walker-cessions"/><ref name="vz-ma"/>
|align="center"|Change on paper only:<br />]
|-
!scope=row|September 13, 1786
|] surrendered its western claim to the federal government except for its ], though it is unclear how much control they held over the ceded region.{{efn|Connecticut's ceded claim was a strip of land west of 120 miles west of ] (the western border of its ]) stretching to the ], bounded by ] and the southern edge of Massachusetts's western claim, roughly 42°2′ north.<ref name="walker-cessions"/>}}<ref name="vz-ct"/><ref name="vz-cessions">Van Zandt, pp. 47–49</ref>
|align="center"|Change on paper only:<br />]
|-
!scope=row|December 16, 1786
|] ] its claim to western ], though it is unclear if Massachusetts ever held control over the region, as the claim was to the "soil, not the sovereignty".{{efn|Massachusetts's ceded claim was the portion of ] 82 miles west of where the ] left New York, to an unclear western boundary, with one source saying it was as far as one mile east of the ].<ref name="walker-cessions"/>}}<ref name="walker-cessions"/><ref name="vz-ma"/> This land was later known as the ].
|align="center"|Change on paper only:<br />]
|-
!scope=row|July 13, 1787
|The Territory Northwest of the ], ceded earlier by ], was ] and commonly became known as the ].<ref name="vz-oh">Van Zandt, pp. 111–114</ref><ref>, July 13, 1787; (National Archives Microfilm Publication M332, roll 9); Miscellaneous Papers of the Continental Congress, 1774–1789; Records of the Continental and Confederation Congresses and the Constitutional Convention, 1774–1789, Record Group 360; National Archives.</ref>
|]
|-
!scope=row|August 9, 1787
|] ceded its western claim to the federal government,<ref>{{cite book|title=Journals of the Continental Congress, 1774–1789|volume=33 | pages=466–477|url=http://memory.loc.gov/cgi-bin/ampage?collId=lljc&fileName=033/lljc033.db&recNum=83&itemLink=r?ammem/hlaw:@field(DOCID+@lit(jc03317))%230330084&linkText=1|editor=Worthington C. Ford|display-editors=etal}}</ref><ref name="vz-sc"/> though it was a result of inaccurate geography and South Carolina never actually held claim to this land. The claim was of a strip of land between the border of ] and the source of the ] but, unknown at the time, the river originated in North Carolina. The eastern part of this cession would be given to ] in 1802, despite Georgia technically already having claim to the land.<ref>{{Cite journal |last=Cotterill |first=R. S. |date=1925 |title=The South Carolina Land Cession |url=https://www.jstor.org/stable/1889567 |journal=The Mississippi Valley Historical Review |volume=12 |issue=3 |pages=376–384 |doi=10.2307/1889567 |jstor=1889567 |issn=0161-391X}}</ref>
|align="center"|Change on paper only:<br />]
|-
!scope=row|December 7, 1787
|] became the first state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratde.asp
|title=Ratification of the Constitution by the State of Delaware; December 7, 1787
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151220123737/http://avalon.law.yale.edu/18th_century/ratde.asp
|archive-date=December 20, 2015
}}</ref>
|align="center" rowspan=11|''no change to map''
|-
!scope=row|December 12, 1787
|] became the second state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratpa.asp
|title=Ratification of the Constitution by the State of Pennsylvania; December 12, 1787
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151105061228/http://avalon.law.yale.edu/18th_century/ratpa.asp
|archive-date=November 5, 2015
}}</ref>
|-
!scope=row|December 18, 1787
|] became the third state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratnj.asp
|title=Ratification of the Constitution by the State of New Jersey; December 18, 1787
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20150923083203/http://avalon.law.yale.edu/18th_century/ratnj.asp
|archive-date=September 23, 2015
}}</ref>
|-
!scope=row|January 2, 1788
|] became the fourth state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratga.asp
|title=Ratification of the Constitution by the State of Georgia; January 2, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151220224732/http://avalon.law.yale.edu/18th_century/ratga.asp
|archive-date=December 20, 2015
}}</ref>
|-
!scope=row|January 9, 1788
|] became the fifth state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratct.asp
|title=Ratification of the Constitution by the State of Connecticut; January 8, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151107080241/http://avalon.law.yale.edu/18th_century/ratct.asp
|archive-date=November 7, 2015
}}</ref>
|-
!scope=row|February 6, 1788
|] became the sixth state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratma.asp
|title=Ratification of the Constitution by the State of Massachusetts; February 6, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20160209044703/http://avalon.law.yale.edu/18th_century/ratma.asp
|archive-date=February 9, 2016
}}</ref>
|-
!scope=row|April 28, 1788
|] became the seventh state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratme.asp
|title=Ratification of the Constitution by the State of Maryland; April 28, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20150710125028/http://avalon.law.yale.edu/18th_century/ratme.asp
|archive-date=July 10, 2015
}}</ref>
|-
!scope=row|May 23, 1788
|] became the eighth state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratsc.asp
|title=Ratification of the Constitution by the State of South Carolina; May 23, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151108102025/http://avalon.law.yale.edu/18th_century/ratsc.asp
|archive-date=November 8, 2015
}}</ref>
|-
!scope=row|June 21, 1788
|] became the ninth state to ratify the ];<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratnh.asp
|title=Ratification of the Constitution by the State of New Hampshire; June 21, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151105061223/http://avalon.law.yale.edu/18th_century/ratnh.asp
|archive-date=November 5, 2015
}}</ref> at this point, the Constitution became the active governing document of those nine states having ratified the same (per ]).
|-
!scope=row|June 25, 1788
|] became the tenth state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratva.asp
|title=Ratification of the Constitution by the State of Virginia; June 26, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20150822161000/http://avalon.law.yale.edu/18th_century/ratva.asp
|archive-date=August 22, 2015
}}</ref>
|-
!scope=row|July 26, 1788
|] became the eleventh state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratny.asp
|title=Ratification of the Constitution by the State of New York; July 26, 1788
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151024010823/http://avalon.law.yale.edu/18th_century/ratny.asp
|archive-date=October 24, 2015
}}</ref>
|-
!scope=row|February 1789
|], governor of the ], pledged allegiance to ] at the February term of the ] Court, effectively ending the claimed independence of Franklin.<ref name="franklin"/><ref>{{cite book | title=History of the Lost State of Franklin | author=Williams, Samuel C. | year=1933 | url=https://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/America/United_States/_Topics/history/_Texts/WILLSF/home.html | page=230}}</ref>
|align="center"|Unofficial change:<br />]
|-
!scope=row|August 7, 1789
|The ] was reorganized under the ].<ref>{{usstat|1|50}}</ref>
|align="center" rowspan=2|''no change to map''
|-
!scope=row|November 21, 1789
|] became the twelfth state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratnc.asp
|title=Ratification of the Constitution by the State of North Carolina; November 21, 1789
|publisher=The Avalon Project at Yale Law School
|access-date=October 31, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151123223225/http://avalon.law.yale.edu/18th_century/ratnc.asp
|archive-date=November 23, 2015
}}</ref>
|-
!scope=row|April 2, 1790
|] ceded its western half to the federal government.{{efn|The new North Carolina–federal border was, from the north, southwest along various ridges of the ]; however, issues caused surveyors to eventually run a line roughly due south rather than continue along the ridge.<ref name="vz-nc"/>}}<ref>{{usstat|1|106}}</ref><ref name="vz-tn"/>
|]
|-
!scope=row|May 26, 1790
|The land recently ceded by ] was organized as the Territory South of the River Ohio, commonly known as the ].<ref name="vz-tn">Van Zandt, pp. 109–111</ref><ref>{{usstat|1|123}}</ref>
|]
|-
!scope=row|May 29, 1790
|] became the thirteenth state to ratify the ].<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/ratri.asp
|title=Ratification of the Constitution by the State of Rhode Island; May 29, 1790
|publisher=The Avalon Project at Yale Law School
|access-date=October 30, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151122110326/http://avalon.law.yale.edu/18th_century/ratri.asp
|archive-date=November 22, 2015
}}</ref>
|align="center"|''no change to map''
|-
!scope=row|December 6, 1790
|Per the ], the ] relocated to ] for ten years until a ] was built and ready.<ref name="capitals"/><ref name="histcaps"/><ref>{{usstat|1|130}}</ref>
|align="center"|]
|-
!scope=row|March 4, 1791
|], which had been considered part of ] despite ] since 1777, was admitted as the fourteenth state.{{efn|The new New York–Vermont border was, from the north: ], the ], then south following borders of townships.<ref name="vz-vt"/>}}<ref name="vz-vt">Van Zandt, pp. 64–65</ref><ref>{{usstat|1|191}}</ref>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|March 30, 1791
|The ], a ] planned to house the federal government by 1800, was ] from land ceded by ] and ],<ref>{{usstat|1|130}}, {{usstat|1|214}}</ref><ref name="vz-dc"/> consisting of a 100 square mile diamond, with its southern tip at ], straddling the ]. However, it was not yet given that name, being simply referred to as the federal district. In September 1791, the commissioners in charge of planning the city would term it the "Territory of Columbia", and various laws refer to a District of Columbia, but sometimes informally. The area does not appear to have been formally named "District of Columbia" until at least the ].<ref>{{cite journal
| last = Tindall
| first = William
| date = February 25, 1919
| title = Naming the Seat of Government of the United States: A Legislative Paradox
| journal = Records of the Columbia Historical Society
| publisher = Historical Society of Washington, D.C.
| volume = 23
| jstor = 40067136
| pages = 10–25
}}</ref> Since the name "Columbia" was used from very early on, and at least informally by the government, the map will use "District of Columbia" starting from this date.
|]
|-
!scope=row|March 3, 1792
|] purchased the ] from the federal government.<ref name="vz-pa"/>
|]
|-
!scope=row|June 1, 1792
|The western half of ], which the state had agreed in 1789 to cede to the federal government,<ref> {{webarchive|url=https://web.archive.org/web/20160624063836/http://law.lis.virginia.gov/compacts/compact-and-boundary-with-kentucky/ |date=June 24, 2016 }}</ref> was admitted as the fifteenth state, ].{{efn|The new Kentucky–Virginia border was, from the south: north along the ] and ] to the ]; northeast to the ]; then down that to the ] and to the ].<ref name="vz-ky"/>}}<ref>{{usstat|1|189}}</ref><ref name="vz-ky">Van Zandt, p. 111</ref>
|]
|-
!scope=row|June 12, 1792
|The Delaware State enacted a ], renaming itself the ].<ref>{{cite book | title=The Federal and State Constitutions, Colonial Charters, and Other Organic Laws of the States, Territories, and Colonies Now or Heretofore Forming the United States of America | url=https://books.google.com/books?id=bWeHAAAAMAAJ | publisher=] | author = Thorpe, Francis Newton | year=1906 | page=568 | access-date=October 26, 2009 | isbn=0-89941-792-2}}</ref>
|align="center" rowspan=3|''no change to map''
|-
!scope=row|August 3, 1795
|Representatives of the United States and the ] sign the ], ending the ] and ceding most of the modern state of ] to United States control.<ref>{{cite web |author1=Hemenway Eric |author2=Little Traverse Bay Bands of Odawa Indians |title=Summer 1795: The Treaty of Greenville creates an uneasy peace |publisher=] |url=https://www.nps.gov/articles/a-long-legacy.htm |access-date=21 April 2020}}</ref>
|-
!scope=row|February 29, 1796
|] ] to abandon several forts in the northwest that it still occupied, including ]. The Jay Treaty also provided for commissions to determine the border between the ] and the ] of the ], and which river to consider the ].<ref>{{cite web|url=https://www.loc.gov/rr/program/bib/ourdocs/jay.html |title=Jay's Treaty |publisher=] |access-date=November 2, 2015 |url-status=live |archive-url=https://web.archive.org/web/20151027175250/http://www.loc.gov/rr/program/bib/ourdocs/jay.html |archive-date=October 27, 2015 }}</ref>
|-
!scope=row|April 25, 1796
|The northern half of ] was ] by ], resolving the dispute over the region.<ref>{{cite web
|url=http://avalon.law.yale.edu/18th_century/sp1795.asp
|title=Treaty of Friendship, Limits, and Navigation Between Spain and The United States; October 27, 1795
|publisher=The Avalon Project at Yale Law School
|access-date=October 30, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20151112201043/http://avalon.law.yale.edu/18th_century/sp1795.asp
|archive-date=November 12, 2015
}}</ref><ref>Van Zandt, p. 22</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|June 1, 1796
|The ] was admitted as the sixteenth state, ].<ref name="vz-tn"/><ref>{{usstat|1|491}}</ref>
|]
|-
!scope=row|April 7, 1798
|In response to the ], an act authorized President ] to appoint commissioners to negotiate with ] about ceding its western land. The act created ] from the southwestern quarter of Georgia in the region recently ceded by ], while maintaining that Georgia still held rights over the territory.<ref>{{usstat|1|549}}</ref><ref name="vz-ms">Van Zandt, pp. 105–106</ref>
|]
|-
!scope=row|October 25, 1798
|Commissioners agreed on the source of the ], setting the lower portion of the border between ] and ] and, thus, where the eastern north–south line originated.<ref>Van Zandt, p. 12</ref>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|June 9, 1800
|] ceded its ] to the federal government, which assigned it to the ].<ref>{{usstat|2|56}}</ref> The act doing so was passed in Congress on April 28, 1800, and Connecticut approved it on this date.<ref>{{cite web|url=https://books.google.com/books?id=CYYUAAAAYAAJ&pg=PA216 |access-date=October 29, 2015 |title=Proclamation of President Adams Accepting the Political Rights over Western Reserve |url-status=live |archive-url=https://web.archive.org/web/20160604034131/https://books.google.com/books?id=CYYUAAAAYAAJ&pg=PA216&lpg=PA216&source=bl&ots=K-c5I4qKCp&sig=rmrPzarb-hblPLq843V2PumJZpA&hl=en&sa=X&ved=0CB8Q6AEwAWoVChMIidPC-q_pyAIVgzomCh345Asw |archive-date=June 4, 2016 |year=1916 }}</ref>
|]
|-
!scope=row|July 4, 1800
|] was organized from the western half of ].{{efn|The new Indiana Territory–Northwest Territory border was, from the south, a line from the mouth of the ] to ], then north.<ref name="vz-in"/>}}<ref>{{usstat|2|58}}</ref><ref name="vz-in">Van Zandt, pp. 114–115</ref>
|]
|-
!scope=row|November 17, 1800
|The ] moved to ] in the ], now built and ready to be the capital.<ref name="capitals"/> This was two weeks before the December 1 date established in the ]; President ] urged Congress to move early in hopes of securing enough Southern votes to be re-elected, though this failed.<ref>{{citation |author=Carter II, Edward C. |title=Benjamin Henry Latrobe and the Growth and Development of Washington, 1798–1818 |journal=Records of the Columbia Historical Society |date=1971–1972 |pages=139}}</ref>
|align="center"|]
|-
!scope=row|January 1, 1801
|The ] ] with the ], renaming itself the ].<ref>{{cite web|url=http://www.rahbarnes.demon.co.uk/Union/Union1800.htm |title=The Acts of Union, 1800 |access-date=November 10, 2015 |archive-url=https://web.archive.org/web/20150923173434/http://www.rahbarnes.demon.co.uk/Union/Union1800.htm |archive-date=September 23, 2015 }}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|February 27, 1801
|The ] was ].<ref name="vz-dc"/><ref>{{usstat|2|103}}</ref>
|align="center"|''no change to map''
|-
!scope=row|April 26, 1802
|] ceded its western half, known as the ], to the federal government.{{efn|The new Georgia–federal border was, from the south, up the ] to its great bend (near ]), then a line from there towards and past ]. The border's description said it would go until it reached the ], and follow that up the river to ], but the river lay entirely within Tennessee.<ref name="vz-ga"/>}} At the same time, the federal government ceded to Georgia the eastern portion of the land previously ceded by ], though in reality Georgia technically already held title to the land, as the description of the earlier cession was based on an erroneous understanding of geography.<ref name="vz-ga"/>
|]
|-
!scope=row|March 1, 1803
|The southern half of the ], along with a thin sliver of ], was admitted as the seventeenth state, ]. The remainder of the Northwest Territory was transferred to Indiana Territory.<ref>{{usstat|2|173}}</ref><ref name="vz-oh"/> The western border was a line due north from the mouth of the ]; the federal definition of the northern border was a line drawn east from the southern tip of ], whereas the Ohio Constitution stated the line should run from the southern tip of Lake Michigan to the most northerly cape of ], essentially the western tip of ]. The confusion caused by these varying descriptions of the state's borders, combined with inaccurate knowledge of geography, as no one at the time knew just how far south Lake Michigan extended, would lead to the ].
|]
|-
!scope=row|November 3, 1803
|The border between ] and ] was resurveyed and established, ending the dispute over that part of the border. The border between ] and ], despite following the original survey, remained vaguely defined.<ref name="tn-va-border"/><ref>{{ussc|name=Virginia v. Tennessee|volume=148|page=503|year=1893}}</ref>
|]
|-
!scope=row|November 30, 1803
|The "]" was transferred from ] to ], to put to rest long-standing disagreements over the border between the two states.<ref name="vz-ma"/> The final report of the commissioners was delivered this day;<ref>{{Cite book |url=https://cdm15019.contentdm.oclc.org/digital/collection/p128501coll3/id/37257 |title=Resolves and private laws of the state of Connecticut | pages=1540–1544 | volume=2 |language=en}}</ref> it is unclear when the change formally occurred.
|]
|}


==1803–1818 (Purchase of Louisiana)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
The southeastern portion of ] was admitted as the 17th state, ]. The remainder of Northwest Territory was transferred to ]. (Note that ] did not pass a resolution formally admitting Ohio; while this was not required, this was retroactively remedied on ] ].)
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|December 20, 1803
|The United States ] ] from ]. This is the date of the formal turnover in ]; the purchase was completed on April 30, 1803.<ref name="vz-louisianapurchase"/> The transfer would be recognized in ] in ] on March 10, 1804, known as ].


The acquisition expanded the United States to the whole of the ] basin,{{efn|There was some question as to whether the purchase also included the basins of the ] and the ], but the question was not relevant before the ] definitively settled the border. Maps universally show the purchase including the Missouri River basin but excluding the Red River basin.<ref name="vz-louisianapurchase"/>}} but the extent of what constituted Louisiana in the south was disputed with ]: the United States claimed the purchase included the part of ] west of the ], whereas Spain claimed it ended at the western border of West Florida;{{efn|The western border of West Florida was a series of waterways, mainly the ], ], and ] Rivers, and Lakes ] and ].<ref name="vz-floridapurchase"/>}}<ref name="vz-floridapurchase"/> and the southwestern border with ] was ], as the United States claimed the ] as the border, but Spain maintained it was the ] and others.<ref name="vz-louisianapurchase"/>
]
|align="center"|]<br /><br />Disputes:<br />
;] ]
]
The ] was made, doubling the country's size. There was a dispute with West Florida over how much land east of the ] it included. The purchase extended slightly north of the modern borders, as it was defined only as the watershed of the Mississippi River.
|-
{{-}}
!scope=row|March 27, 1804
|The land between ] and ] previously ceded by ] was assigned to Mississippi Territory.<ref name="vz-ms"/><ref>{{usstat|2|303}}</ref>
|]
|-
!scope=row|October 1, 1804
|] was organized from the ] south of ], with the remainder being designated the ] and placed under the jurisdiction of ].<ref>{{usstat|2|283}}</ref><ref name="vz-la">Van Zandt, pp. 106–108</ref>
|]
|-
!scope=row|June 30, 1805
|] was organized from ], north of a line east from the southern tip of ], and east of a line north from the lake's northern tip.<ref>{{usstat|2|309}}</ref><ref name="vz-mi">Van Zandt, pp. 127–128</ref> The southeastern portion of the border technically conflicted with the definition of ], which claimed the ] north of that line; however, the exact position of Lake Michigan was not yet known.
|]
|-
!scope=row|July 4, 1805
|The ] was organized as ].<ref name="vz-la"/><ref>{{usstat|2|331}}</ref>
|]
|-
!scope=row|March 1, 1809
|] was organized from the western half of ].{{efn|The new Illinois Territory&ndash;Indiana Territory border was, from the south, the ] up to ], then north.<ref name="vz-il"/>}}<ref>{{usstat|2|514}}</ref><ref name="vz-il">Van Zandt, pp. 116–117</ref>
|]
|-
!scope=row|September 26, 1810
|The ] declared independence from ], claiming the area of ] west of the ]. It maintained some control over its territory.<ref name="west-florida">{{cite web|url=http://www.independent.org/publications/working_papers/article.asp?id=1478 |title="Not Merely Perfidious but Ungrateful": The U.S. Takeover of West Florida |publisher=Independent Institute |author=Higgs, Robert |access-date=June 14, 2016 |archive-url=https://web.archive.org/web/20160523091425/http://www.independent.org/publications/working_papers/article.asp?id=1478 |archive-date=May 23, 2016 }}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|December 10, 1810
|Armed forces led by ] took possession of the portion of ] west of the ], following a proclamation on October 27, 1810, by President ] to do so. The United States had considered the region part of the ], including the area which had revolted against ] and formed the ]. Madison's proclamation stated that it was to be "taken as part" of ].<ref name="vz-floridapurchase"/><ref name="vz-louisianapurchase">Van Zandt, pp. 23–26</ref><ref>{{cite web |url=http://millercenter.org/president/madison/speeches/speech-3610 |title=Proclamation—Occupation of West Florida (October 27, 1810) |publisher=] |access-date=October 29, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20151030015016/http://millercenter.org/president/madison/speeches/speech-3610 |archive-date=October 30, 2015 }}</ref> The land west of Mobile Bay to the Pearl River was occupied and annexed ''de facto'' by the military in 1811.<ref name="Cox">{{cite book|title=The West Florida Controversy, 1798–1813 – a Study in American Diplomacy|author=Cox, Isaac Joslin | publisher=The Johns Hopkins Press|location = Baltimore, Maryland| date=1918|url=https://archive.org/details/westfloridacont00coxgoog|author-link=Isaac Joslin Cox }}</ref>{{rp|2a}}<sup>()</sup>
|align="center"|Disputes:<br />]
|-
!scope=row|April 30, 1812
|Most of ] was admitted as the eighteenth state, ].{{efn|The northwestern remainder of Orleans Territory presumably rejoined Louisiana Territory, as its extent was still vaguely defined.}}<ref name="vz-la"/><ref>{{usstat|2|701}}</ref> The southeastern remainder presumably became unorganized territory, as it had no definition for a short time.
|]
|-
!scope=row|May 14, 1812
|The claimed portion of ] east of the ] was assigned to ], though the area around Mobile Bay remained under the control of ].<ref name="vz-ms"/><ref>{{usstat|2|734}}</ref> The United States militarily occupied Mobile and the surrounding area up to the ] in April 1813.
|]
|-
!scope=row|June 4, 1812
|Since its name was now shared with the state of ], ] was renamed ].<ref>{{usstat|2|743}}</ref><ref name="vz-mo">Van Zandt, pp. 117–118</ref>
|]
|-
!scope=row|August 4, 1812
|The remaining claimed portion of ], west of the ], was added to ], following the assent of that state to an act passed by Congress on April 14, 1812.<ref>{{usstat|2|708}}</ref><ref>{{cite book | title=A General Digest of the Acts of the Legislature of Louisiana: Passed from the Year 1804, to 1827, Inclusive | page=9 | url=https://books.google.com/books?id=L25GAQAAIAAJ&pg=RA1-PA9 | access-date=October 28, 2015| author1=Louisiana | last2=Lislet | first2=Louis Moreau | year=1828 }}</ref>
|]
|-
!scope=row|August 16, 1812
|During the ], the garrison at ] ], leading the ] to occupy ], the capital and population center of ].<ref name="fortdetroit">{{cite web|url=http://www.history.com/this-day-in-history/detroit-surrenders-without-a-fight |title=Detroit surrenders without a fight |publisher=The History Channel |access-date=June 13, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160519093110/http://www.history.com/this-day-in-history/detroit-surrenders-without-a-fight |archive-date=May 19, 2016 }}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|September 29, 1813
|The British withdrew from ] following the ], allowing American forces to regain control over ].<ref name="fortdetroit"/><ref>{{Citation
| last = Farmer
| first = Silas
| year = 1884
| title = The History of Detroit and Michigan: Or, the Metropolis Illustrated
| publisher = S. Farmer
| location = Detroit
| url = https://books.google.com/books?id=RH9FDeAyUJ4C
| oclc = 359750
| page=224
}}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|August 24, 1814
|] forces ], but are forced to withdraw the next day. The functions of the capital were only momentarily suspended, though President ] took refuge in ].<ref>{{cite web |url=http://townofbrookevillemd.org/about/town-history/ |title=Town History |publisher=Town of Brookville, Maryland |access-date=June 13, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160505183341/http://townofbrookevillemd.org/about/town-history/ |archive-date=May 5, 2016 }}</ref>
|align="center"|''no change to map''
|-
!scope=row|December 11, 1816
|The southern part of ], along with small parts of ] and ], were admitted as the nineteenth state, ].{{efn|Indiana was defined as the territory north of the ] and east of the ], but while the territory's line turned north at ], the state's border continued up the Wabash until it reached the point where a line drawn north from Post Vincennes would last intersect the river as it weaved back and forth. The northern border of the state was a line east from 10 miles north of the southern tip of ], until it reached the meridian that formed ]'s western border, which was a line drawn north from the mouth of the ].<ref name="vz-in"/>}} The remainder of Indiana Territory across ] became unorganized territory.<ref name="vz-in"/><ref>{{usstat|3|289}}, {{usstat|3|399}}</ref>
|]
|-
!scope=row|March 3, 1817
|] was organized from the eastern half of ].{{efn|The new Alabama Territory&ndash;Mississippi Territory border was, from the north: up the ] to Bear Creek (around today's ]); a line to the northwestern corner of ]; then south.<ref name="vz-al"/>}}<ref>{{usstat|3|371}}</ref><ref name="vz-al">Van Zandt, pp. 108–109</ref>
|]
|-
!scope=row|December 10, 1817
|] was admitted as the twentieth state, ].<ref name="vz-ms"/><ref>{{usstat|3|348}}, {{usstat|3|472}}</ref>
|]
|-
!scope=row|February 6, 1818
|] created ] with a description that inadvertently overlapped with ]. It described the border of the county as running "a due west course to, the Tombeckbe river; thence up the same to the Cotton Gin Port".<ref> {{webarchive|url=https://web.archive.org/web/20160304202515/http://www.legislature.state.al.us/aliswww/history/acts_and_journals/Acts_1818_Jan-Feb/Page3_pgs_11-20.html |date=March 4, 2016 }}</ref> Unknown at the time, the origin of the ] and ] were in Mississippi.
|align="center"|Change on paper only:<br />]
|-
!scope=row|June 30, 1818
|Per the terms of the ] ending the ], the ] returned ] to ], and the United States returned ], ], and ] to the United Kingdom, all of which were captured from the other side during the war.<ref>{{cite book | url=https://archive.org/details/maineinnortheas00burrgoog | title=Maine in the Northeastern Boundary Controversy | publisher=State | author=Burrage, Henry Sweetser | year=1919 | access-date=June 22, 2016 | page=}}</ref>
|align="center"|''no change to map''
|-
!scope=row|December 3, 1818
|The half of ] south of 42°30′ north was admitted as the twenty-first state, ]. The remainder of the territory, along with the unorganized territory that was recently part of ], was assigned to ].<ref name="vz-il"/><ref>{{usstat|3|428}}, {{usstat|3|536}}</ref>
|]
|}


==1819–1845 (Northwest expansion)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
The unorganized land ceded by ] was added to ].
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|January 30, 1819
|The ] went into effect, setting ] as the border with the ] west of the ], and also establishing the ] as a shared region with the United Kingdom.<ref name="vz-1818">Van Zandt, pp. 14–15</ref><ref>{{usstat|8|248}}</ref><ref>{{cite web|url=https://2009-2017.state.gov/documents/organization/83046.pdf |title=Treaties in Force |publisher=] |access-date=July 14, 2015 }}</ref> Oregon Country had no defined northern limit, but it can be assumed that it did not encroach much upon ]; this map uses the later-established line at ] for simplicity.
|align="center"|]<br /><br />Northwestern North America:<br />]
|-
!scope=row|July 4, 1819
|] was organized from the southern slice of ].{{efn|The new Arkansaw Territory&ndash;Missouri Territory border was, from where the ] meets ]: west to the ], up that to ], then west.<ref name="vz-mo"/>}}<ref>{{usstat|3|493}}</ref><ref name="vz-ar">Van Zandt, pp. 118–120</ref>
|]
|-
!scope=row|December 14, 1819
|] was admitted as the twenty-second state, ].<ref name="vz-al"/><ref>{{usstat|3|489}}, {{usstat|3|608}}</ref> The statehood act provided for a survey of the southern part of the border with ], which was intended to be north–south, for adjustment if it was discovered to encroach upon Mississippi's established counties; it was later discovered to do so.
|]
|-
!scope=row|March 15, 1820
|As part of the ], the ], the northern and separate part of ], was admitted as the twenty-third state, ].<ref>{{usstat|3|544}}</ref><ref name="vz-me">Van Zandt, pp. 55–60</ref>
|]
|-
!scope=row|April 21, 1820
|This is the earliest known date of the name "]" being officially used instead of "Arkansaw Territory".<ref>{{usstat|3|565}}</ref>
|]
|-
!scope=row|May 12, 1820
|The border between ] and ] was established. To make up for the fact that the border between the ] and the ] veered north as much as almost 10 miles from ], a new survey was conducted starting at that latitude on the ] and moving east to the Tennessee River, hence guaranteeing this last bit of border would fit the original ideal.<ref name="tn-va-border"/>
|]
|-
!scope=row|July 19, 1820
|The overlap of the longitudinal southern border between ] and ] was resolved, as per the act admitting Alabama as a state, because the provisional border encroached on Mississippi.<ref name="vz-al"/><ref>{{cite book | title=The Official and Statistical Register of the State of Mississippi, Volume 4 | url=https://books.google.com/books?id=pLC0kgvJJG4C&pg=PA57 | pages=57–58 | access-date=November 23, 2015| last1=Rowland | first1=Dunbar | year=1917 }}</ref> As the result of a survey, the southern border terminus was moved about 3.8 miles to the east, which changed the border up to the then-northwest corner of Alabama's Washington County. The date when this happened is unclear; the sources available give either an unpublished report dated May 29, 1820, or the completion of the demarcation of the new line on July 19, 1820.
|align="center"|Change on paper only:<br />]
|-
!scope=row|December 19, 1820
|] redefined some county borders, ending its erroneous overlap of ] created on February 6, 1818.<ref>{{Cite book |author=Alabama Legislature |url=http://archive.org/details/acts-1820 |title=Alabama legislative acts, 1820 | year=1820 | page=92}}</ref>
|align="center"|Change on paper only:<br />]
|-
!scope=row|February 22, 1821
|The ] with ] took effect.<ref name="vz-floridapurchase">Van Zandt, pp. 26–27</ref> The many changes included:
* The border with the holdings of Spain was concretely defined; previously, it had been the watershed of the ] and, for ], the ], whereas now it followed specific rivers and parallels.{{efn|The new border was, from the ]: up the ] to ]; north to the ]; up that to ]; north to the ]; up that to its source; north to ]; then west to the ].<ref name="vz-floridapurchase"/>}}
* The new border placed the "]" in ].
* ] was ceded to the United States, although the formal transfer would not happen until July.
* ] had created ] south of the ], and this area was now on the Spanish side of the border. However, as this was a change made solely by the territory, and not by the federal government, in this map it is considered a domestic dispute.
* With ] being ceded, the dispute between it and ], ], and ] was resolved.
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|July 10, 1821
|] was formally transferred to the United States by ].<ref name="fl-transfer">{{cite web|url=https://www.floridamemory.com/blog/2012/07/17/9-the-united-states-formally-takes-control-of-florida/ |title=The United States Formally Takes Control of Florida (July 17, 1821) |access-date=July 14, 2015 |publisher=State Library and Archives of Florida |url-status=live |archive-url=https://web.archive.org/web/20150908071907/http://www.floridamemory.com/blog/2012/07/17/9-the-united-states-formally-takes-control-of-florida/ |archive-date=September 8, 2015 }}</ref>
|]
|-
!scope=row|July 17, 1821
|] was formally transferred to the United States by ].<ref name="fl-transfer"/>
|]
|-
!scope=row|August 10, 1821
|The southeastern corner of ] was admitted as the twenty-fourth state, ], the rest becoming unorganized territory.{{efn|The new Missouri&ndash;federal border was, from the mouth of the ]: up the river to a point west of the ] on the ], west to a point north of the mouth of the ], then south.<ref name="vz-mo"/>}}<ref name="vz-mo"/><ref>{{usstat|3|545}}</ref>
|]
|-
!scope=row|March 30, 1822
|The former ] and ] were organized as ].<ref>{{usstat|3|654}}</ref><ref name="vz-fl">Van Zandt, pp. 104–105</ref>
|]
|-
!scope=row|May 26, 1824
|The half of ] west of a line south from a point 40 miles west of ]'s western border was returned to unorganized territory.<ref name="vz-ar"/><ref>{{usstat|4|40}}</ref>
|]
|-
!scope=row|January 12, 1825
|A ] with the ] established ] as the northern border of ] for American purposes; a separate treaty created the same border between Russia and the ].<ref>{{cite web|url=http://www.explorenorth.com/library/history/bl-rusus1825.htm |title=Convention Between the United States of America and His Majesty the Emperor of All the Russias, Relative to Navigating, Fishing, Etc., in the Pacific Ocean |access-date=January 3, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160319221147/http://www.explorenorth.com/library/history/bl-rusus1825.htm |archive-date=March 19, 2016 }}</ref> As this was likely the ''de facto'' border anyway, the region is already mapped with this line.
|align="center"|''no change to map''
|-
!scope=row|May 6, 1828
|A treaty with the ] moved the western border of ], returning part of it to unorganized territory.{{efn|The new Arkansas Territory&ndash;federal border, from the north, a line from the southwestern corner of ] to a point on the ] "100 paces east" of ], as the border of the lands of the ], then south.<ref name="vz-ar"/> However, the ] determined in 1909 that the "100 paces east" was a clerical error, and that logically it should have said "100 paces west".<ref>{{cite book | url=https://books.google.com/books?id=if02AQAAMAAJ | title=Arkansas Reports: Cases Determined in the Supreme Court of Arkansas, Volume 93 | pages=168&ndash;171 | year=1910 | access-date=April 5, 2019| last1=Supreme Court | first1=Arkansas | last2=Williams | first2=George W. }}</ref>}}<ref name="vz-ar"/><ref>{{usstat|7|311}}</ref>
|]
|-
!scope=row|January 20, 1831
|King ], having been asked per the ] to arbitrate the disputed border between ] and the ], rendered his decision: since reconciling the treaty with the maps given was too difficult, he drew a compromise line. The British government accepted it, but Maine protested, and on January 19, 1832, the American government rejected it.<ref>Van Zandt, pp. 15-17</ref>
|align="center"|''no change to map''
|-
!scope=row|July 9, 1832
|The region of ] north of the ], which was disputed with the ], declared independence as the ].<ref name="indianstream">{{cite journal
| last = Keedy
| first = Edwin R.
| date = January 1953
| title = The Constitutions of the State of Franklin, the Indian Stream Republic and the State of Deseret
| journal = University of Pennsylvania Law Review
| volume = 101
| number = 4
| jstor = 3309935
| pages = 521–525
| doi = 10.2307/3309935
| url = https://scholarship.law.upenn.edu/cgi/viewcontent.cgi?article=7935&context=penn_law_review
}}</ref> While tiny, it does appear to have maintained some control over its territory.
|align="center"|Disputes:<br />]
|-
!scope=row|June 28, 1834
|] gained a large parcel of land from unorganized territory, extending west to the ] and ].<ref name="vz-mi"/><ref>{{usstat|4|701}}</ref>
|]
|-
!scope=row|August 5, 1835
|The ] recognized the jurisdiction of ], thus ending its claimed independence. The date given is of a communication sent to ] authorities;<ref>{{cite book | url=https://books.google.com/books?id=HhwfAQAAMAAJ | title=British and Foreign State Papers | year=1852 | page=444 | access-date=June 28, 2016| last1=Foreign Office | first1=Great Britain }}</ref> other sources note a resolution passed by the citizens of Indian Stream on April 2, 1836.<ref name="indianstream"/>
|align="center"|Disputes:<br />]
|-
!scope=row|June 15, 1836
|] was admitted as the twenty-fifth state, ].<ref name="vz-ar"/><ref>{{usstat|5|50}}</ref>
|]
|-
!scope=row|July 3, 1836
|] was organized from the western bulk of ].{{efn|The new Michigan Territory&ndash;Wisconsin Territory border was, from ]: up the ] to ]; a line to the source of the ]; then down that to ]. However, this definition was impossible: The Montreal River ended long before it reached Lac Vieux Desert. The issue would be resolved in 1850.<ref name="vz-mi"/>}}<ref>{{usstat|5|10}}</ref><ref name="vz-wi">Van Zandt, pp. 128–131</ref> The two large peninsulas between the ] remained in Michigan Territory; the ] was included in exchange for the territory abandoning its claim to the ]. The territory initially rejected this plan, but would accept it on December 14.
|]
|-
!scope=row|December 14, 1836
|] agreed to abandon its claim to the ], ending its dispute with ].<ref>{{cite web |url=https://mittenhistory.com/2013/12/14/the-frostbitten-convention-or-how-michigan-ended-the-toledo-war-and-became-a-state/ |title=The Frostbitten Convention; or, How Michigan Ended the Toledo War and Became a State |access-date=June 22, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160809123756/https://mittenhistory.com/2013/12/14/the-frostbitten-convention-or-how-michigan-ended-the-toledo-war-and-became-a-state/ |archive-date=August 9, 2016 }}</ref>
|]
|-
!scope=row|January 26, 1837
|] was admitted as the twenty-sixth state, ].<ref name="vz-mi"/><ref>{{usstat|5|144}}</ref>
|]
|-
!scope=row|March 28, 1837
|The ], obtained from several nations including the ], ], ], ], and ],<ref>{{cite journal | last=Combs | first=H. Jason | year=2002 | title=The Platte Purchase and Native American Removal | jstor=25669782 | journal=Plains Anthropologist | volume=47 | issue=182 | pages=265–274| doi=10.1080/2052546.2002.11932095 | s2cid=163783522 }}</ref> transferred some land from unorganized territory to northwest ], extending its northern border west to the ].<ref name="vz-mo"/><ref>{{usstat|5|34}}, {{usstat|5|802}}</ref>
|]
|-
!scope=row|July 3, 1838
|] was organized from ] west of the ].<ref>{{usstat|5|235}}</ref><ref name="vz-ia">Van Zandt, pp. 131–133</ref>
|]
|-
!scope=row|February 11, 1839
|] claimed an area north of its ] with ], initiating the long dispute known as the ].<ref>, accessed March 16, 2023</ref>
|]
|-
!scope=row|May 21, 1840
|Surveying conducted along the border with ] concluded that the area claimed by ] for ] belonged to Texas.<ref>{{usstat|5|674}}</ref>
|align="center"|]
|-
!scope=row|November 10, 1842
|The ] defined the border with the ] east of the ].<ref>{{cite web
|url=https://avalon.law.yale.edu/19th_century/br-1842.asp
|title=Text of "The Webster–Ashburton Treaty"
|publisher=The Avalon Project at Yale Law School
|access-date=December 3, 2023
}}</ref><ref>Van Zandt, pp. 17–18</ref> One source also mentions it very slightly altering the maritime boundary between Michigan and Wisconsin Territory.<ref>{{cite web|url=https://www.lib.msu.edu/exhibits/map/minnsliver.jsp |title=Evolution of Michigan's Boundaries: The Minnesota Sliver |publisher=] |access-date=December 27, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160108184914/https://www.lib.msu.edu/exhibits/map/minnsliver.jsp |archive-date=January 8, 2016 }}</ref> The treaty resolved the disputes over the northern borders of ] and ],{{efn|The new northeastern border was, from ]: up the ] to its source; north to the ]; up that to the ]; up that to its source outlet at ]; southwest to the northwest branch of the St. John River; a line from there to where the St. John River crosses 46°25’ north; up the river to its source; along the highlands to the source of ], then down that to ].<ref name="vz-me"/><ref name="vz-nh"/>}} the northeastern border of ],{{efn|The new northern border was, from ]: up the ] to the many lakes and rivers of the ], eventually reaching the ]; then down that to the ].<ref name="vz-mn"/>}} and ] with ].


The border between ] and ] on the one side, and the United Kingdom on the other, was clarified by the treaty. In 1816, construction began on an unnamed fort nicknamed "]" on a peninsula in ] that, while south of the surveyed border, was discovered to be north of ], which was the border set by the ] and thus in British territory. Consequently, construction on the fort was abandoned. The Webster–Ashburton Treaty specified that section of the border was to follow the surveyed line, rather than the exact parallel, thus moving the fort's area into the United States, and a new fort, ], would be built on the spot in 1844.<ref>Text from Webster–Ashburton Treaty: "till the line thus run intersects the old line of boundary surveyed and marked by Valentine and Collins previously to the year 1774, as the 45th degree of north latitude, and which has been known and understood to be the line of actual division between the States of New York and Vermont on one side, and the British Province of Canada on the other"</ref> As the earlier line was surveyed, even though it did not match the definition, it was deemed to be the legitimate border.
]
|align="center"|]<br /><br />Disputes:<br />]
;] ]
|-
The ] was split into the ], which was under the authority of ], and the organized ]. The western border of Orleans Territory caused further conflict with ] over which river was the western boundary of the Purchase.
!scope=row|July 5, 1843
{{-}}
|Local settlers created a ] for ]. While not official, it did maintain some jurisdiction over the area.<ref>{{cite web|url=https://sos.oregon.gov/archives/records/provisional-guide/Pages/oregon-maps.aspx |title=Provisional and Territorial Records Guide – 1843 Map |publisher=Oregon State Archives |access-date=March 12, 2016}}</ref>
|align="center"|Unofficial change: ]
|-
!scope=row|March 3, 1845
|] was admitted as the twenty-seventh state, ].<ref name="vz-fl"/><ref>{{usstat|5|742}}</ref>
|]
|}


==1845–1860 (Southwest expansion)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
] was split from ], including the whole of the lower peninsula of present-day ] but only the portion of the upper peninsula held by the ] after Indiana Territory had been split from it.<ref name="NWT"></ref>
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|December 29, 1845
|The ] was ] and admitted as the twenty-eighth state, ], extending the United States southwest to the ].<ref>{{usstat|9|108}}</ref><ref name="vz-tx">Van Zandt, pp. 120–127</ref> All of Texas was claimed by ]. While many sources state that Mexico recognized the independence of the eastern portion of Texas, ] were rejected by the Mexican government. Texas formally handed over sovereignty to the United States in a ceremony on February 19, 1846.<ref name="texasstate">{{cite web|url=https://history.state.gov/countries/texas |title=A Guide to the United States' History of Recognition, Diplomatic, and Consular Relations, by Country, since 1776: Texas |publisher=] |access-date=April 3, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170401084304/https://history.state.gov/countries/texas |archive-date=April 1, 2017 }}</ref> The annexation led to the beginning of the ] a few months later.<ref name="texasstate"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|June 15, 1846
|The ] established ] west of the ] as the continental border (so it did not include ]) with land held by the ]. The sharing of ] ended, and the United States portion became unorganized territory.<ref>{{cite web
|url=http://avalon.law.yale.edu/19th_century/br-1846.asp
|title=Text of "Treaty with Great Britain, in Regard to Limits Westward of the Rocky Mountains"
|publisher=The Avalon Project at Yale Law School
|access-date=August 4, 2006
|url-status=live
|archive-url=https://web.archive.org/web/20090419184450/http://avalon.law.yale.edu/19th_century/br-1846.asp
|archive-date=April 19, 2009
}}</ref>


The treaty was vague on which strait should be the border between Vancouver Island and the continent, thus causing a dispute over ownership of the ].<ref name="vz-18"/> It specified "through the middle of the said channel and of Fuca Straits, to the Pacific Ocean".
]
|align="center"|]<br /><br />Northwestern North America:<br />]<br /><br />Disputes:<br />]
;] ]
|-
The ] was organized as ].
!scope=row|September 22, 1846
{{-}}
|Following the ] on August 18, 1846, of ], the capital of the ] territory of ],<ref>{{cite book | url=https://books.google.com/books?id=4SOSEswVAEEC&pg=PA129 | title=A Journey Through New Mexico History | author=Lavash, Donald | access-date=March 16, 2016 | year=2006 | page=129| publisher=Sunstone Press | isbn=978-0-86534-541-6 }}</ref> a code of laws known as the ] was created for the area.<ref>{{cite web|url=http://avalon.law.yale.edu/19th_century/kearney.asp |title=New Mexico – Laws for the Government of the Territory of New Mexico; September 22, 1846 |access-date=March 16, 2016 |publisher=The Avalon Project at Yale Law School |url-status=live |archive-url=https://web.archive.org/web/20160401184136/http://avalon.law.yale.edu/19th_century/kearney.asp |archive-date=April 1, 2016 }}</ref><ref>{{cite web|url=https://www.raremaps.com/gallery/detail/35381?view=print |title=(James S. Calhoun's Annotated Copy) Map of the Territory of New Mexico Made by Order of Brig. Gen. S.W. Kearny under Instructions from Lieut. W.H. Emory, U.S.T.E. by Lieut's J.W. Abert and W.G. Peck, U.S.T.E., 1846–7 |year=1850 |access-date=March 16, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160818150540/https://www.raremaps.com/gallery/detail/35381?view=print |archive-date=August 18, 2016 }}</ref> The region overlapped with ]' claim, though Texas had little to no control over the area outside of its eastern quarter.
|align="center"|Unofficial change:<br />]
|-
!scope=row|December 28, 1846
|The portion of ] south of 43°30′ north and east of the ] was admitted as the twenty-ninth state, ]. The remainder became unorganized territory.<ref name="vz-ia"/><ref>{{usstat|9|117}}</ref>
|]
|-
!scope=row|March 13, 1847
|The ] ] ] back to ].<ref name="vz-dc">Van Zandt, pp. 88–92</ref> Congress passed the act on July 9, 1846,<ref>{{usstat|9|35}}</ref> residents of Alexandria County were proclaimed by the president to have agreed to it on September 7, 1846,<ref>{{usstat|9|1000}}</ref> and Virginia took possession of the land on this date.<ref> {{webarchive|url=https://web.archive.org/web/20160510045250/https://books.google.com/books?id=arlOAQAAIAAJ&lpg=PA41&ots=gqgVPUPY25&pg=PA41 |date=May 10, 2016 }}</ref>
|]
|-
!scope=row|May 29, 1848
|The southern bulk of ] was admitted as the thirtieth state, ].{{efn|The new Wisconsin&ndash;Wisconsin Territory border was, from ]: up the ] to its first rapids; south to the ]; then down that to the ].<ref name="vz-wi"/>}} The remainder became unorganized territory.<ref name="vz-wi"/><ref>{{usstat|9|233}}</ref> However, the citizens of the remainder decided to continue on with a civil government, and even elected a delegate to the United States House of Representatives who would be seated on January 15, 1849, essentially making this region a ''de facto'' continuation of Wisconsin Territory.<ref>{{cite book|url=https://archive.org/details/henryhastingssib00willrich |title=Henry Hastings Sibley: A Memoir |year=1894 |pages=–281 |author=Williams, J. Fletcher |publisher=Minnesota Historical Society |access-date=December 28, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160307002027/https://archive.org/details/henryhastingssib00willrich |archive-date=March 7, 2016 }}</ref>
|]
|-
!scope=row|July 4, 1848
|The ] ended the ] and ceded a ] from ], consisting of its territories of ] and ], and its claim to ].{{efn|The new international border was, from the ]: along the southern and western border of New Mexico until it meets the ]; down that to the ]; then a line to a point one league south of the port of ]. However, the southern border of New Mexico was in question, with the US claim being 31°52′ north, and the Mexican claim being 32°22′ north.<ref name="vz-cession"/>}}<ref>{{usstat|9|922}}</ref> A border dispute began over a disagreement about the southern border of Santa Fe de Nuevo México.<ref name="vz-cession">Van Zandt, pp. 28–29</ref>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|August 14, 1848
|] was organized from the unorganized territory that was formerly part of ].<ref>{{usstat|9|323}}</ref><ref name="vz-or">Van Zandt, pp. 153–155</ref>
|]
|-
!scope=row|February 13, 1849
|The boundary dispute between ] and ] known as the ] was ] by the ]. The resulting border was the ] that existed before the dispute, roughly splitting the two claims.<ref name="honey">{{ussc|name=Missouri v. Iowa|volume=48|page=660|year=1849}}</ref>
|]
|-
!scope=row|March 3, 1849
|] was organized from the region that had been operating as ''de facto'' ], and unorganized territory east of the ] and ] Rivers.<ref>{{usstat|9|403}}</ref><ref name="vz-mn">Van Zandt, pp. 133–134</ref>
|]
|-
!scope=row|March 12, 1849
|A local government formed the ] and claimed a vast portion of the southwest, including most of the ]. Though it petitioned to be admitted to the United States, the proposal was rejected and, in 1850, ] was formed instead.<ref>{{cite encyclopedia | title=Young, Brigham | encyclopedia=Encyclopedia of Politics of the American West | page=675 | access-date=January 28, 2016 | url=https://books.google.com/books?id=UCRzAwAAQBAJ&pg=PA675| isbn=978-1-4522-7606-9 | last1=Danver | first1=Steven L | date=April 25, 2013}}</ref> The claimed area overlapped slightly with ]' claimed area, as well as part of ].
|align="center"|Unofficial change:<br />]
|-
!scope="row"|November 24, 1849
|], with consent from the United States Congress,<ref name="usstat|9|245">{{usstat|9|245}}</ref> extended its border with ] from the west bank of the ] to the middle of the river.<ref name="usstat|9|245"/><ref>{{cite web |title=Boundaries | url=https://tshaonline.org/handbook/online/articles/mgb02 |work=Handbook of Texas Online |publisher=Texas State Historical Association |access-date=May 10, 2019}}</ref><ref>{{cite journal | last=Andrew | first=Bunyan H. | year=1949 | title=Some Queries Concerning the Texas-Louisiana Sabine Boundary | jstor=30240685 | journal=The Southwestern Historical Quarterly | volume=53 | issue=1 | pages=1–18 }}</ref><ref>{{ussc|394|1}}</ref>
|align="center"|''no change to map''
|-
!scope=row|September 9, 1850
|The western portion of the ] was admitted as the thirty-first state, ].{{efn|The new California&ndash;federal border was, from the north: south along ] to ]; a line to where the ] intersects ]; then down the Colorado River.<ref name="vz-ca"/>}}<ref name="vz-ca">Van Zandt, pp. 151–153</ref><ref>{{usstat|9|452}}</ref> The portion of the remainder north of ] and west of the summit of the ] was organized as ].<ref>{{usstat|9|453}}</ref><ref name="vz-ut">Van Zandt, pp. 159–160</ref> Part of Utah Territory overlapped with the portion of ] that would be purchased on December 13, 1850, but the law authorizing the purchase was passed on this day, so the borders of Utah Territory assumed that the purchase would go through.
|]
|-
!scope=row|December 9, 1850
|The ] ceded less than one acre of underwater rock for a ] in ] near ]; although it was on Middle Reef, it was named for the nearby Horseshoe Reef.<ref>{{Cite web |title=Buffalo Water Intake, Horseshoe Reef Light Historical Marker |url=https://www.hmdb.org/m.asp?m=85227 |access-date=2024-03-25 |website=www.hmdb.org |language=en}}</ref> It was surrounded by British waters, thus creating a form of enclave.<ref name="horseshoe">, signed April 11, 1908; accessed June 30, 2015</ref>
|]
|-
!scope=row|December 13, 1850
|The federal government purchased the western claims of ].{{efn|The new Texas&ndash;federal border was, from the south: up the ] to ]; east to ]; north to ]; then east.<ref name="vz-tx"/>}}<ref name="vz-tx"/> ] was organized from the part of this land east of the ], along with the remaining unorganized territory from the ].{{efn|The new New Mexico Territory&ndash;federal border was, from 36°30′ north and 103° west: north to ]; then west to the summit of the ] (called then the Sierra Madre).<ref name="vz-nm"/>}}<ref>{{usstat|9|446}}</ref><ref name="vz-nm">Van Zandt, pp. 160–165</ref> New Mexico Territory included all of the area that had been governed under the ].
|]
|-
!scope=row|April 5, 1851
|The ] dissolved itself, its functions and territory largely having been superseded by ].<ref>{{cite book | url=https://archive.org/details/lawsordinancesof00dese | title=Laws and ordinances of the state of Deseret (Utah) | publisher=Shepard Book Co. | year=1919 | access-date=June 22, 2016 | page=Prefatory| author1=Deseret }}</ref>
|align="center"|Unofficial change:<br />]
|-
!scope=row|March 2, 1853
|] was organized from the half of ] north of ] and the ].<ref>{{usstat|10|172}}</ref><ref name="vz-wa">Van Zandt, pp. 155–156</ref>
|]
|-
!scope=row|May 30, 1854
|] was organized from unorganized territory north of ], and ] was organized north of ].<ref>{{usstat|10|277}}</ref><ref name="vz-ks">Van Zandt, pp. 138–139</ref><ref name="vz-ne">Van Zandt, pp. 136–138</ref> Much of the remaining unorganized territory, east of ], became known as ], designated as a place to resettle Indian tribes.


A small strip between the ] and Kansas Territory was unclaimed because it fell south of Kansas Territory's border but north of ], which had been established in the ] as the northern limit of slavery, and thus Texas could not have it. This became known as the ], or sometimes "No Man's Land".<ref>Kenneth R. Turner, , {{webarchive|url=https://web.archive.org/web/20150402160744/http://www.okhistory.org/publications/enc/entry.php?entry=NO001 |date=April 2, 2015}} Encyclopedia of Oklahoma History and Culture, www.okhistory.org (accessed June 4, 2015).</ref>
]
|]
;] ]
|-
] was split from ]. Indiana Territory included the present-day borders of ]; since its western and eastern borders continued northward, it also included portions of the upper peninsula of Michigan and the ] of present-day ].<ref name="NWT" />
!scope=row|June 30, 1854
{{-}}
|The United States purchased a large parcel from ] known as the ], as it offered a much better route for a southern transcontinental railroad.{{efn|The new international border was, starting from where the ] crosses 31°47′ north: west 100 miles; south to 31°20′ north; west to ]; a line to a point on the ] 20 miles below the mouth of the ]; then up the Colorado River.<ref name="vz-gadsden"/>}}<ref name="vz-gadsden">Van Zandt, p. 29</ref><ref>{{cite web|url=http://avalon.law.yale.edu/19th_century/mx1853.asp |title=Gadsden Purchase Treaty : December 30, 1853 |publisher=The Avalon Project at Yale Law School |access-date=June 3, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150519020643/http://avalon.law.yale.edu/19th_century/mx1853.asp |archive-date=May 19, 2015 }}</ref> This resolved the border dispute, since the disputed land was included in the purchase.<ref name="vz-cession"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|August 4, 1854
|The recently obtained ] was assigned to ].<ref name="vz-nm"/><ref>{{usstat|10|575}}</ref>
|]
|-
!scope=row|January 11, 1855
|] was transferred from ] to ] because it was inaccessible from the rest of the Massachusetts.<ref>{{usstat|10|602}}</ref><ref>Van Zandt, p. 70</ref><ref>{{cite book | title=Report of the Regents of the University on the Boundaries of the State of New York, Volume II | url=https://books.google.com/books?id=_BQzAQAAIAAJ&pg=PA219 | access-date=July 9, 2015 | pages=219–223| year=1884 }}</ref>
|]
|-
!scope=row|March 6, 1855
|The Supreme Court ruled in favor of ] in a boundary dispute with ], setting the state boundary line along ].<ref name=case>{{cite court|litigants=]|vol=58|reporter=U.S.|opinion=478|pinpoint=480|court=US|date=1854|url=http://supreme.justia.com/us/58/478/case.html}}</ref>
|align="center"|''no change to map''
|-
!scope=row|October 28, 1856
|] and ] were claimed under the ].<ref name="guano"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|May 11, 1858
|The eastern half of ] was admitted as the thirty-second state, ].{{efn|The new Minnesota&ndash;federal border was, from the north: up the ] to the ]; up that to ] and its southern tip; a line to ] and through that to its southern tip; then south.<ref name="vz-mn"/>}} The remainder became unorganized territory.<ref name="vz-mn"/><ref>{{usstat|11|285}}</ref>
|]
|-
!scope=row|August 31, 1858
|] was claimed under the ].<ref name="guano"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|December 3, 1858
|] was claimed under the ].<ref name="guano"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|February 14, 1859
|The western half of ] was admitted as the thirty-third state, ].{{efn|The new Oregon&ndash;Washington Territory border was, from the north, up the ] to the mouth of the ], then south.<ref name="vz-or"/>}} The remainder was transferred to ].<ref name="vz-or"/><ref>{{usstat|11|383}}</ref>
|]
|-
!scope=row|July 6, 1859
|A team of surveyors created the "Middleton Offset", a small notch in the border between ] and ]. It is unknown exactly why this was done, though one theory is a local landowner wanted his property in Tennessee.<ref>{{cite encyclopedia | encyclopedia=The Kentucky Encyclopedia | title=Middleton Offset | url=https://books.google.com/books?id=8eFSK4o--M0C&q=simpson+county+offset&pg=PA635 | access-date=October 28, 2015 | page=635| isbn=0-8131-2883-8 | last1=Kleber | first1=John E | year=1992 }}</ref><ref name="kytn">{{cite web|url=http://www.sitemason.com/files/kuec92/tnkyborder.pdf |title=Tennessee-Kentucky border didn't turn out as straight as it was supposed to be |access-date=October 28, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160304084356/http://www.sitemason.com/files/kuec92/tnkyborder.pdf |archive-date=March 4, 2016 }}</ref>
|]
|-
!scope=row|September 6, 1859
|] was claimed under the ],<ref name="guano"/> though it had been claimed by ] in 1858.<ref name="doi-johnston"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|November 7, 1859
|A local government was set up encompassing parts of the territories of ], ], ], ], and ], with the name of ].{{efn|The claimed borders of Jefferson Territory were between ], ], ], and ].<ref name="jefferson-territory"/>}} While never recognized by the federal government, it generally held control over the area until ] was established, which adopted most of its laws.<ref name="jefferson-territory">{{Cite journal |jstor = 1832884|title = The Territory of Colorado|journal = The American Historical Review|volume = 12|issue = 1|pages = 53–65|last1 = Paxson|first1 = Frederic L.|year = 1906|doi = 10.2307/1832884}}</ref>
|align="center"|Unofficial change:<br />]
|-
!scope=row|December 27, 1859
|], ], ], and ] were claimed under the ].<ref name="guano"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|December 29, 1859
|] and ] were claimed under the ].<ref name="guano"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|February 8, 1860
|] created ], claiming part of ] based on a different understanding from the federal government of which fork of the ] was the border between the two.<ref name="greer"/>


], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], and ] were all claimed under the ].<ref name="guano"/> Many additional islands were listed as bonded on this date, but based on the coordinates they were either phantoms or duplicates. In addition, ] was claimed, which may have existed and would be sighted as late as 1917, but has since disappeared.<ref>{{cite news|url=https://news.google.com/newspapers?nid=110&dat=19321016&id=34VOAAAAIBAJ&pg=2584,3552314|title=Vanishing of Sarah Ann, Tiny Pacific Island, Causes Scientists Much Worry|date=October 16, 1932|publisher=Lundington Daily News|page=1|location=Washington|access-date=January 13, 2010}}</ref>
==1810s==
|align="center"|]<br /><br />Pacific Ocean:<br />]
]
|}
;] ]
The United States annexed the portion of ] that declared independence as the Republic of West Florida. Also, sometime during 1810, the ] was formed.
{{-}}


==1860–1865 (Civil War)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
] was admitted as the 18th state, ].
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|December 20, 1860
|In response to the ] of ], ] proclaimed its secession from the Union, withdrawing from the Congress of the United States.<ref name="secession"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|January 9, 1861
|] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|January 10, 1861
|] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|January 11, 1861
|] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|January 19, 1861
|] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|January 26, 1861
|] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/> However, the ] and ] congressional districts, around ], maintained representation in Congress.
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|January 29, 1861
|The bulk of ] east of ] was admitted as the thirty-fourth state, ]. The remainder became unorganized territory.<ref name="vz-ks"/><ref>{{usstat|12|126}}</ref>
|]
|-
!scope=row|February 8, 1861
|The ] was formed by representatives of the seceded states of ], ], ], ], ], and ].<ref> {{webarchive|url=https://web.archive.org/web/20160820151934/http://docsouth.unc.edu/imls/19conf/19conf.html |date=August 20, 2016 }}, accessed July 8, 2015</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|February 28, 1861
|] was organized from portions of ], ], and ], along with unorganized territory.{{efn|The borders of Colorado Territory were parallels ] and ], and ] ] and ].<ref name="vz-co"/>}}<ref>{{usstat|12|172}}</ref><ref name="vz-co">Van Zandt, pp. 141–144</ref>
|]
|-
!scope=row|March 2, 1861
|] proclaimed its secession from the Union and was admitted to the ],<ref name="secession"/><ref> {{webarchive|url=https://web.archive.org/web/20160820151934/http://docsouth.unc.edu/imls/19conf/19conf.html |date=August 20, 2016 }}, accessed July 8, 2015</ref> withdrawing from Congress.


] was organized from ] and the unorganized territory north of it.{{efn|The new Nebraska Territory&ndash;Dakota Territory border was, from the east: up the ] to the ]; up that to the ]; up that to ]; then west.<ref name="vz-ne"/>}} Nebraska Territory's western border was moved to 33° west from Washington, gaining small portions of ] and ].<ref name="vz-ne"/><ref>{{usstat|12|239}}</ref><ref name="vz-dakota">Van Zandt, pp. 134–136</ref> ] was organized from ] west of ].<ref>{{usstat|12|209}}</ref><ref name="vz-nv">Van Zandt, pp. 158–159</ref>
]
|align="center"|]<br /><br />Disputes:<br />]
;] ]
|-
The federal government added the newly-annexed land of ] to ].
!scope=row|March 28, 1861
{{-}}
|Representatives in the southern half of ] proclaimed an independent ] south of ].<ref>{{cite web|url=https://www.nps.gov/cwindepth/statebystate/Arizona.html |title=Arizona Territory |access-date=April 5, 2017 |publisher=] |url-status=live |archive-url=https://web.archive.org/web/20170406111850/https://www.nps.gov/cwindepth/statebystate/Arizona.html |archive-date=April 6, 2017 }}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|April 17, 1861
|Following the ] and President ]'s ], ] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/> However, the ] (along the ]), ] (near ]), and ], ], and ] (in the northwest of the state) congressional districts maintained representation in Congress.
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|May 6, 1861
|] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/>
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|May 7, 1861
|] was admitted to the ].<ref> {{webarchive|url=https://web.archive.org/web/20160820151934/http://docsouth.unc.edu/imls/19conf/19conf.html |date=August 20, 2016 }}, accessed July 8, 2015</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|May 16, 1861
|] ] itself neutral in the ].
|align="center"|''no change to map''
|-
!scope=row|May 20, 1861
|] was admitted to the ].<ref> {{webarchive|url=https://web.archive.org/web/20160820151934/http://docsouth.unc.edu/imls/19conf/19conf.html |date=August 20, 2016 }}, accessed July 8, 2015</ref>


] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession"/>
]
|align="center"|]<br /><br />Disputes:<br />]
;] ]
|-
], having the same name as a state, was renamed to ].
!scope=row|May 21, 1861
{{-}}
|] was admitted to the ]. The law admitting the state required a presidential proclamation before it was to take effect,<ref> {{webarchive|url=https://web.archive.org/web/20160820151934/http://docsouth.unc.edu/imls/19conf/19conf.html |date=August 20, 2016 }}, accessed June 29, 2016</ref> which sources say took place on this date;<ref>{{cite web | url=http://northcarolinahistory.org/encyclopedia/secession/ | title=Secession | publisher=John Locke Foundation}}</ref> the only primary source found so far is a statement from ] on July 20 stating that the proclamation had been made.<ref>Confederate Congress 1861, 1:272. ()</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|June 6, 1861
|], governor of ], declared the territory disbanded and handed over the government to the first governor of ].<ref name="jefferson-territory"/>
|align="center"|Unofficial change:<br />]
|-
!scope=row|June 8, 1861
|] proclaimed its secession from the Union, withdrawing from Congress.<ref name="secession">{{cite web|url=http://www.digitalhistory.uh.edu/disp_textbook.cfm?smtID=3&psid=3953 |title=Secession Ordinances of 13 Confederate States |publisher=] |access-date=May 24, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150905091739/http://www.digitalhistory.uh.edu/disp_textbook.cfm?smtID=3&psid=3953 |archive-date=September 5, 2015 }}</ref> However, the ], ], and ] congressional districts in the central part of the state maintained representation in Congress.
|align="center"|]<br /><br />Disputes:<br />]
|-
!scope=row|June 25, 1861
|The federal government recognized the ] in ] as the legitimate government of ].<ref>{{cite news|url=https://www.nytimes.com/1864/06/26/news/virginia-the-restored-government-of-virginia-history-of-the-new-state-of-things.html?pagewanted=all |work=The New York Times |title=VIRGINIA.; The Restored Government of Virginia—History of the New State of Things |date=June 26, 1864 |url-status=live |archive-url=https://web.archive.org/web/20160812201924/http://www.nytimes.com/1864/06/26/news/virginia-the-restored-government-of-virginia-history-of-the-new-state-of-things.html?pagewanted=all |archive-date=August 12, 2016 }}</ref>
|align="center"|]
|-
!scope=row|July 2, 1861
|] was admitted to the ].<ref>{{cite book | url=https://books.google.com/books?id=APs7AQAAMAAJ | title=Official Records of the Union and Confederate Navies in the War of the Rebellion | page=103 | access-date=June 22, 2016 | year=1922| last1=Navy Dept | first1=United States | last2=Rush | first2=Richard }}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|August 1, 1861
|Following Confederate victory in the ], ] was proclaimed as part of the ].<ref>{{cite book |title=The Civil War in the Western Territories |last=Colton |first=Ray Charles |year=1985 |publisher=University of Oklahoma Press |isbn=0-8061-1902-0 |pages=122–123 |url=https://books.google.com/books?id=JdMnyfgENN0C |access-date=August 3, 2010}}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|September 13, 1861
|Following the Confederate occupation of ], ], on September 3, 1861, the state abandoned neutrality and aligned with the Union government.<ref> {{webarchive|url=https://web.archive.org/web/20161221110639/https://books.google.com/books?id=zzhNAQAAMAAJ&pg=PA110 |date=December 21, 2016 }}</ref>
|align="center"|''no change to map''
|-
!scope=row|October 31, 1861
|A splinter government in ], proclaimed the secession of the state from the United States.<ref name="secession"/>
|align="center"|Disputes:<br />]
|-
!scope=row|November 20, 1861
|A convention in ], proclaimed the formation of a splinter government in ] and the secession of ] from the United States.<ref name="secession"/>
|align="center"|Disputes:<br />]
|-
!scope=row|November 28, 1861
|The splinter ] of ] was admitted to the ]. The Confederate States never held much power over the state, but it was given full representation in the legislature.<ref>Confederate Public Law ; accessed May 22, 2015</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|December 10, 1861
|The splinter ] of ] was admitted to the ]. The Confederate States never held much power over the state, but it was given full representation in the legislature.<ref>Confederate Public Law {{webarchive|url=https://web.archive.org/web/20160421231551/https://books.google.com/books?id=eMhthJ3G9ykC&lpg=PR12pg%3DPA222 |date=April 21, 2016 }}; accessed May 22, 2015</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|December 21, 1861
|The ] ratified treaties with the ], and the ] and ].<ref name="csaindiantreaties">{{cite web|url=http://treatiesportal.unl.edu/csaindiantreaties/ |title=As long as grass shall grow and water run: The treaties formed by the Confederate States of America and the tribes in Indian Territory, 1861 |publisher=] |access-date=May 2, 2017 |url-status=live |archive-url=https://web.archive.org/web/20161024162044/http://treatiesportal.unl.edu/csaindiantreaties/ |archive-date=October 24, 2016 }}</ref><ref name="dougdawgz">{{cite web|url=http://dougdawg.blogspot.com/2010/10/maps-and-history-of-oklahoma-county.html |title=Maps and History of Oklahoma County 1830–1900 |date=28 October 2010 |access-date=May 2, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170414222429/http://dougdawg.blogspot.com/2010/10/maps-and-history-of-oklahoma-county.html |archive-date=April 14, 2017 }}</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|December 23, 1861
|The ] ratified treaties with the ], granting them a delegate to the ], and with the ], granting them a delegate to be shared with the ].<ref name="csaindiantreaties"/><ref name="dougdawgz"/>
|align="center"|Disputes:<br />]
|-
!scope=row|December 31, 1861
|The ] ratified treaties with the ] and ], granting them a delegate in the ]; with the ]; with the ], granting them a delegate to be shared with the ]; and the ].<ref name="csaindiantreaties"/><ref name="dougdawgz"/>
|align="center"|Disputes:<br />]
|-
!scope=row|March 1, 1862
|A decree by the ] took effect, modifying the border between ] and ].{{efn|The decree transferred land from the left bank of the ] to Rhode Island, including what is now ], in exchange land around ] being transferred to Massachusetts.<ref name="vz-ma"/>}}<ref name="vz-ma"/><ref>{{usstat|11|382}}</ref>
|]
|-
!scope=row|April 15, 1862
|] was annexed by ], and the American claim falls dormant.<ref name="doi-palmyra">{{cite web|url=https://www.doi.gov/oia/islands/palmyraatoll |publisher=] |title=Palmyra Atoll |date=11 June 2015 |access-date=July 8, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150910204050/https://www.doi.gov/oia/islands/palmyraatoll |archive-date=September 10, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|July 14, 1862
|The slice of ] west of 38° ] was transferred to ].<ref name="vz-nv"/><ref>{{usstat|12|575}}</ref>
|]
|-
!scope=row|December 30, 1862
|The ] were claimed under the ].<ref name="guano"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|February 24, 1863
|] was organized from the half of ] west of ].<ref name="vz-az">Van Zandt, p. 165</ref><ref>{{usstat|12|664}}</ref>
|]
|-
!scope=row|March 3, 1863
|] was organized from the parts of ] and ] west of ], and the half of ] east of the ] and a line north from the mouth of the ].<ref>{{usstat|12|808}}</ref><ref name="vz-id">Van Zandt, pp. 156–158</ref>
|]
|-
!scope=row|March 4, 1863
|Because of a disruption in voting and low turnout, no one was allowed to take the seats in the ] held by the Unionist areas of ], ], and ], effectively expelling the states.<ref>Martis, Kenneth C., "Historical Atlas of Political Parties in the United States Congress: 1789-1989, 1989 {{ISBN|0-02-920170-5}} p. 116.</ref>
|]
|-
!scope=row|June 20, 1863
|The northwestern counties of ], represented by the ] in ], were split from the rest of Virginia and admitted to the Union as the thirty-fifth state, ].{{efn|The Virginia counties that became West Virginia were: ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], ], and ].<ref name="vz-wv"/>}}<ref>{{usstat|13|731}}</ref><ref name="vz-wv">Van Zandt, pp. 95–96</ref> The Restored Government of Virginia was relocated to ].
|]
|-
!scope=row|August 5, 1863
|] was transferred by the federal government from ] to ].<ref>W.Va. Acts 1863, 1st sess., ch. 35, sec. 1/ {{webarchive|url=https://web.archive.org/web/20160406125119/https://books.google.com/books?id=QRtEAAAAYAAJ&lpg=RA1-PA103&ots=x_zuvvEvgk&pg=RA3-PA33 |date=April 6, 2016 }}</ref>
|]
|-
!scope=row|November 2, 1863
|] was transferred from ] to ].<ref>W.Va. Acts 1863, 1st sess., ch. 90, sec. 1/ {{webarchive|url=https://web.archive.org/web/20160522145407/https://books.google.com/books?id=QRtEAAAAYAAJ&lpg=RA1-PA103&ots=x_zuvvEvgk&pg=RA1-PA103 |date=May 22, 2016 }}</ref>
|]
|-
!scope=row|May 26, 1864
|] was organized from the northeast third of ],{{efn|The new Idaho Territory&ndash;Montana Territory border was, from the north: south along ] to the crest of the ] and the ]; then along that to the new tripoint with ].<ref name="vz-mt"/>}} and the southeast third of Idaho Territory was transferred to ].{{efn|The new Dakota Territory&ndash;Idaho Territory border was, from the south: north along ] to the crest of the ], then northwest along that to the new tripoint with ].<ref name="vz-dakota"/>}}<ref name="vz-mt">Van Zandt, pp. 145–151</ref><ref name="vz-dakota"/><ref>{{usstat|13|85}}</ref>
|]
|-
!scope=row|October 15, 1864
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|October 31, 1864
|] was admitted as the thirty-sixth state, ].<ref name="vz-nv"/><ref>{{usstat|13|749}}</ref>
|]
|-
!scope=row|May 5, 1865
|The ] cabinet met in ], and dissolved.<ref>{{cite web|url=http://www.civilwaronthewesternborder.org/timeline/remaining-confederate-cabinent-dissolves |title=Remaining Confederate Cabinet Dissolves |publisher=Kansas City Public Library |access-date=May 21, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160303215240/http://www.civilwaronthewesternborder.org/timeline/remaining-confederate-cabinent-dissolves |archive-date=March 3, 2016 }}</ref> Military surrenders were scattered throughout 1865, but the most important is regarded as that of the ] following the ] on April 9.
|align="center"|Disputes:<br />]
|}


==1866–1897 (Reconstruction and western statehood)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
Some sources indicate that the southern portion of ] was made unorganized.<ref name="statoids"></ref>
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|May 5, 1866
|The slice of ] west of ] was transferred to ].<ref name="usstat|14|43">{{usstat|14|43}}</ref>
|]
|-
!scope=row|July 24, 1866
|] was readmitted to Congress.<ref>{{usstat|14|364}}</ref>
|]
|-
!scope=row|December 26, 1866
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|January 18, 1867
|The northwestern corner of ], west of the ] and ], was transferred to ]. The law transferring the land was approved May 5, 1866, but unlike the ] transfer of that day, this transfer was contingent on the state accepting it.<ref name="usstat|14|43"/><ref>{{cite book|title=First Biennial Report of the Nevada Historical Society |date=1909 |url=https://books.google.com/books?id=MvQ7AAAAIAAJ&pg=PA133 |page=133 |access-date=May 21, 2015 |last1=Society |first1=Nevada State Historical |url-status=live |archive-url=https://web.archive.org/web/20160418231841/https://books.google.com/books?id=MvQ7AAAAIAAJ&pg=PA133 |archive-date=April 18, 2016 }}</ref>
|]
|-
!scope=row|March 1, 1867
|] was admitted as the thirty-seventh state, ].<ref name="vz-ne"/><ref>{{usstat|14|820}}</ref>
|]
|-
!scope=row|July 1, 1867
|] was formed from several British colonies, including ], thus inheriting the dispute over ] and ].
|align="center"|Disputes:<br />]
|-
!scope=row|August 28, 1867
|] was claimed.<ref name="doi-acquisition"/> An attempt had been made at the time of its discovery in 1859 to claim it under the ].<ref>{{cite book |author=Hawaii. Dept. of the Attorney General |title=Opinions of the Attorney General of Hawaii |publisher=Paradise of the Pacific Press |date=1925 |page=244 |url=https://books.google.com/books?id=0kwwAQAAMAAJ&pg=PA244}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|October 18, 1867
|] was ] from the ] and designated the ].{{efn|The borders of the Department of Alaska were, from the ]: Up the ] to ]; then along the "summit of the mountains situated parallel to the coast" (the definition of which was disputed) to ]; then north.<ref name="vz-akboundary"/>}}<ref name="vz-ak">Van Zandt, pp. 165–166</ref><ref name="alaskapurchase">{{cite web
|url=http://avalon.law.yale.edu/19th_century/treatywi.asp
|title=Treaty concerning the Cession of the Russian Possessions in North America by his Majesty the Emperor of all the Russias to the United States of America
|publisher=The Avalon Project at Yale Law School
|access-date=August 4, 2006
|url-status=live
|archive-url=https://web.archive.org/web/20090129101148/http://avalon.law.yale.edu/19th_century/treatywi.asp
|archive-date=January 29, 2009
}}</ref> A vague description and lack of quality surveying made the southeastern border with ] holdings ].<ref name="vz-akboundary"/>
|align="center"|Northwestern North America:<br />]
|-
!scope=row|June 22, 1868
|] was readmitted to Congress.<ref>{{usstat|15|72}}</ref>
|]
|-
!scope=row|June 25, 1868
|] was readmitted to Congress.<ref>Act authorizing readmission on ratification of 14th amendment: {{usstat|15|73}}. Florida ratified the amendment before that law was passed, so Florida was readmitted upon passage of the law.</ref>
|]
|-
!scope=row|July 4, 1868
|] was readmitted to Congress.<ref>Act authorizing readmission on ratification of 14th amendment: {{usstat|15|73}}. Proclamation of North Carolina's ratification: {{usstat|15|703}}.</ref>
|]
|-
!scope=row|July 9, 1868
|] and ] were readmitted to Congress.<ref>Act authorizing readmission on ratification of 14th amendment: {{usstat|15|73}}. Proclamations of Louisiana's and South Carolina's ratification: {{usstat|15|704}}.</ref>


] was claimed by the ].<ref name="uk-chrono"/>
]
|align="center"|]<br /><br />Pacific Ocean:<br />]
;] ]
|-
The southern portion of ] was admitted as the 19th state, ]. The remainder becomes unorganized.
!scope=row|July 13, 1868
{{-}}
|] was readmitted to Congress.<ref>Act authorizing readmission on ratification of 14th amendment: {{usstat|15|73}}. Proclamation of Alabama's ratification: {{usstat|15|704}}.</ref>
|]
|-
!scope=row|July 25, 1868
|] was readmitted to Congress.<ref>{{cite book|url=https://books.google.com/books?id=LwMI1Xokv7AC&pg=PA172 |title=The Empire State of the South |author=Meyers, Christopher C. |isbn=978-0-88146-111-4 |access-date=May 19, 2015 |year=2008 |publisher=Mercer University Press |url-status=live |archive-url=https://web.archive.org/web/20160521041454/https://books.google.com/books?id=LwMI1Xokv7AC&lpg=PA172&pg=PA172 |archive-date=May 21, 2016 }}</ref>


] was organized from portions of ], ], and ] Territories.{{efn|The borders of Wyoming Territory were parallels ] and ], and ] ] and ].<ref name="vz-wy"/>}}<ref>{{usstat|15|178}}</ref><ref name="vz-wy">Van Zandt, pp. 144–145</ref> The territory would remain under the jurisdiction of the Dakota Territory until its own government was organized on May 19, 1869.<ref>{{cite web|url=http://www.wyo.gov/about-wyoming/wyoming-history |title=Wyoming History |publisher=State of Wyoming |access-date=November 12, 2015 |url-status=live |archive-url=https://web.archive.org/web/20151108111846/http://www.wyo.gov/about-wyoming/wyoming-history |archive-date=November 8, 2015 }}</ref> The act organizing Wyoming Territory became law on this date, but it is unclear if the territory could be considered "organized" until May 19, 1869, as the act specifies it was not to take effect until a government is organized; however, all sources use this date as the creation, and most use it for the organization, of the territory. A ] of the Dakota Territory was erroneously left behind on the western side of Wyoming Territory.<ref name="vz-dakota-remnant"/>
]
|]
;] ]
|-
] was split from ].
!scope=row|August 12, 1868
{{-}}
|The list of bonded ] mentions "Islands in Caribbean Sea not named" bonded on this date, but it is unknown to what this is referring.<ref name="guano"/>
|align="center"|''no change to map''
|-
!scope=row|December 11, 1868
|] was claimed under the ].<ref name="guano"/> ] has claimed it throughout its history.
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|March 3, 1869
|] was again expelled from Congress following failures of ] in the state.<ref>{{cite EB1911|wstitle= Georgia (United States) |volume= 11 | pages = 751&ndash;758; see page 757 }}</ref>
|]
|-
!scope=row|November 22, 1869
|], ], ], and ] were claimed under the ].<ref name="guano">{{cite web|first=John Bassett |last=Moore |publisher=U.S. Government Printing Office |year=1906 |title=A Digest of International Law as Embodied in Diplomatic Discussions, Treaties and Other International Agreements, International Awards, the Decisions of Municipal Courts, and the Writings of Jurists and Especially in Documents, Published and Unpublished, Issued by Presidents and Secretaries of State of the United States, the Opinions of the Attorneys-General, and the Decisions of Courts, Federal and State |pages=566–580 |url=https://books.google.com/books?id=9mIHAQAAIAAJ&q=morant%20Keys%20guano%20claim%20british&pg=PA566 |location=Washington, DC |url-status=live |archive-url=https://web.archive.org/web/20160501155658/https://books.google.com/books?id=9mIHAQAAIAAJ&dq=morant%20Keys%20guano%20claim%20british&pg=PA566 |archive-date=May 1, 2016 }}</ref><ref name="doi-acquisition">{{cite web|url=https://www.doi.gov/oia/islands/acquisitionprocess |title=Acquisition Process of Insular Areas |date=12 June 2015 |publisher=] ] |access-date=July 15, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160815202029/https://www.doi.gov/oia/islands/acquisitionprocess |archive-date=August 15, 2016 }}</ref> Except for Pedro Cays, ] has claimed them throughout its history.
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|January 26, 1870
|] was readmitted to Congress.<ref>{{usstat|16|62}}</ref>
|]
|-
!scope=row|February 23, 1870
|] was readmitted to Congress.<ref>{{usstat|16|67}}</ref>
|]
|-
!scope=row|March 30, 1870
|] was readmitted to Congress.<ref>{{usstat|16|80}}</ref>
|]
|-
!scope=row|July 15, 1870
|] was again readmitted to Congress.<ref>{{usstat|16|363}}</ref>


The ] was transferred by the ] to ], thus transferring its portion of the ].<ref>{{cite encyclopedia|url=http://www.thecanadianencyclopedia.ca/en/article/northwest-territories/ |title=Northwest Territories |encyclopedia=The Canadian Encyclopedia |access-date=July 6, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150627110823/http://www.thecanadianencyclopedia.ca/en/article/northwest-territories/ |archive-date=June 27, 2015 }}</ref>
]
|align="center"|]<br /><br />Northwestern North America:<br />]
;] ]
|-
] was admitted as the 20th state, ].
!scope=row|February 9, 1871
{{-}}
|A small parcel was transferred from ] to ] following a sudden change in course of the ].<ref name="vz-ne"/><ref>{{usstat|16|93}}</ref>
|]
|-
!scope=row|July 20, 1871
|] joined ], transferring the ] over the ] as well as its portion of the ].<ref>{{cite encyclopedia|url=http://www.thecanadianencyclopedia.ca/en/article/british-columbia/ |title=British Columbia |encyclopedia=The Canadian Encyclopedia |access-date=July 6, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150620093319/http://www.thecanadianencyclopedia.ca/en/article/british-columbia/ |archive-date=June 20, 2015 }}</ref>
|align="center"|Disputes:<br />]<br /><br />Northwestern North America:<br />]
|-
!scope=row|October 21, 1872
|The ] with ] over the ] was resolved in the favor of the United States claim.<ref name="vz-18">Van Zandt, p. 18</ref>
|align="center"|Disputes:<br />]
|-
!scope=row|1873
|] was claimed by the ].<ref>{{cite encyclopedia|title=Vostok Island |encyclopedia=Historical Dictionary of the British Empire |year=2015 |publisher=Rowman & Littlefield |location=] |pages=561–562 |url=https://books.google.com/books?id=WdFbCQAAQBAJ&pg=PA561 |access-date=July 2, 2015 |isbn=978-0-8108-7524-1 |url-status=live |archive-url=https://web.archive.org/web/20160516183754/https://books.google.com/books?id=WdFbCQAAQBAJ&lpg=PP1&pg=PA561 |archive-date=May 16, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|February 17, 1873
|The ] of ] that was left behind when ] was created was transferred to ].<ref name="vz-dakota-remnant">Van Zandt, pp. 136, 149–150</ref><ref>{{usstat|17|464}}</ref>
|]
|-
!scope=row|August 1, 1876
|] was admitted as the thirty-eighth state, ].<ref name="vz-co"/><ref>{{usstat|18|474}}</ref>
|]
|-
!scope=row|August 13, 1877
|The ] created the ], including ] and ].<ref>{{cite encyclopedia|title=Union Islands |encyclopedia=Historical Dictionary of the British Empire |year=2015 |publisher=Rowman & Littlefield |location=] |pages=540–541 |url=https://books.google.com/books?id=WdFbCQAAQBAJ&pg=PA91 |access-date=July 2, 2015 |isbn=978-0-8108-7524-1 |url-status=live |archive-url=https://web.archive.org/web/20160506141517/https://books.google.com/books?id=WdFbCQAAQBAJ&lpg=PP1&pg=PA91 |archive-date=May 6, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|March 3, 1879
|The border across the ] between ] and ] was decided via arbitration. It is unknown if any land actually changed hands.<ref name="vz-md"/>
|align="center"|''too vague to map''
|-
!scope=row|September 8, 1879
|], claimed by ]; the ]; and ], claimed by ], were claimed by the United States under the ];<ref name="guano"/> according to the Office of Insular Affairs, Serranilla Bank was claimed again on September 13, 1880.<ref name="doi-acquisition"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|April 7, 1880
|A very small area of ], was transferred to ] in response to a change in the course in the ].<ref name="vz-vt"/><ref>{{usstat|21|72}}</ref>
|align="center"|''too small to map''
|-
!scope=row|September 13, 1880
|], claimed by ], was claimed by the United States under the ].<ref name="guano"/> The list of bonded claims also mentions a "De Anes" island claimed on this date, with coordinates matching ]; however, the same list points out that the claim to "Aves Island" was found to be invalid.
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|1881
|] was claimed by the ].<ref>{{cite encyclopedia|title=Flint Island |encyclopedia=Historical Dictionary of the British Empire |year=2015 |publisher=Rowman & Littlefield |location=] |page=191 |url=https://books.google.com/books?id=WdFbCQAAQBAJ&pg=PA191 |access-date=July 2, 2015 |isbn=978-0-8108-7524-1 |url-status=live |archive-url=https://web.archive.org/web/20160512101228/https://books.google.com/books?id=WdFbCQAAQBAJ&lpg=PP1&pg=PA191 |archive-date=May 12, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|May 23, 1882
|The area between ] and the ] and ] Rivers was transferred from ] to ].<ref name="vz-dakota"/><ref>{{usstat|22|35}}</ref> The act was passed in Congress on March 28 and accepted by the Nebraska legislature on this date.<ref>{{cite journal
| last = Watkins
| first = Albert
| date = 1913
| title = Nebraska Territorial Acquisition
| url = https://books.google.com/books?id=j0lHAQAAMAAJ&pg=PA53
| journal = Collections of the Nebraska State Historical Society
| publisher = Nebraska State Historical Society
| volume = XVII
| pages = 53
| access-date= May 18, 2015
}}</ref>
|]
|-
!scope=row|June 1, 1882
|The ] and ] were annexed by the ] to ]; it appears they were no longer claimed by the United States after this.<ref> {{webarchive|url=https://web.archive.org/web/20160417062140/https://books.google.com/books?id=wEIBAAAAYAAJ&pg=PA1601&hl=en&sa=X&ei=dLGHVf3HKIutyQSM3IKAAQ&ved=0CCwQ6AEwAQ |date=April 17, 2016 }}</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|May 17, 1884
|The ] was organized into the ].<ref>{{usstat|23|24}}</ref>
|align="center"|Northwestern North America:<br />]
|-
!scope=row|June 21, 1884
|The ], claimed by ], were claimed under the ].<ref name="guano"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|March 15, 1888
|] was annexed by the ]; it appears the island was no longer claimed by the United States after this.<ref name="fanning-washington"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|March 17, 1888
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|October 26, 1888
|The ] became a protectorate of the ], thus initiating a claim on the atolls of ], ], ], and ].<ref name="uk-chrono">{{cite encyclopedia|title=Chronology |encyclopedia=Historical Dictionary of the British Empire |year=2015 |publisher=Rowman & Littlefield |location=] |pages=xix–xxxviii |url=https://books.google.com/books?id=WdFbCQAAQBAJ&pg=PR19 |access-date=July 4, 2015 |isbn=978-0-8108-7524-1 |url-status=live |archive-url=https://web.archive.org/web/20160408060413/https://books.google.com/books?id=WdFbCQAAQBAJ&lpg=PP1&pg=PR19 |archive-date=April 8, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|May 29, 1889
|] was annexed by the ]; it appears the island was no longer claimed by the United States after this.<ref name="fanning-washington">{{cite journal
| date = 1914
| url = https://books.google.com/books?id=lbgjAQAAIAAJ&q=march+15+1888
| journal = United Empire
| title = Unknown title
| publisher = Royal Colonial Institute
| volume = 4
| pages = 266
| access-date= June 22, 2015
}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|June 3, 1889
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|June 26, 1889
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|June 29, 1889
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|July 10, 1889
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|November 2, 1889
|] was split in half along the "seventh standard parallel north", a few miles south of ], and admitted as the thirty-ninth state, ], and the fortieth state, ].<ref name="vz-dakota"/><ref name="1889states"/>
|]
|-
!scope=row|November 8, 1889
|] was admitted as the forty-first state, ].<ref name="vz-mt"/><ref name="1889states"/>
|]
|-
!scope=row|November 11, 1889
|] was admitted as the forty-second state, ].<ref name="vz-wa"/><ref name="1889states">{{usstat|25|676}}</ref>
|]
|-
!scope=row|May 2, 1890
|] was ] from the ] and the western half of ], except for the ], which would be added later upon cession from the ].{{efn|The new Oklahoma Territory&ndash;federal border was, from where the ] meets ]: north to the ]; down that to ] land; north along that border to the ]; down that to ] land; north and east along that border to ]; then north. This omits the Cherokee Outlet, whose complex borders separated the main portion of Oklahoma Territory from the former Public Land Strip.<ref name="vz-ok"/>}}<ref>{{usstat|26|81}}</ref><ref name="vz-ok">Van Zandt, pp. 139–140</ref>
|]
|-
!scope=row|July 3, 1890
|] was admitted as the forty-third state, ].<ref name="vz-id"/><ref>{{usstat|26|215}}</ref>
|]
|-
!scope=row|July 10, 1890
|] was admitted as the forty-fourth state, ].<ref name="vz-wy"/><ref>{{usstat|26|222}}</ref>
|]
|-
!scope=row|March 8, 1892
|The ] became a protectorate of the ], thus initiating a claim on ] and ].<ref name="uk-chrono"/> No record of a United States claim exists after this point, so it is assumed this is when the claim fell dormant.
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|May 28, 1892
|] was claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|September 16, 1893
|Per a treaty with the ], the federal government purchased the ] in the ] and opened it to settlement, transferring it to ] as provided in the ].<ref name="vz-ok"/><ref>{{usstat|27|640}}</ref>
|]
|-
!scope=row|November 17, 1894
|The ], ], and ] were stricken from the list of claimed ].<ref name="guano"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|January 4, 1896
|] was admitted as the forty-fifth state, ].<ref name="vz-ut"/><ref>{{usstat|28|107}}</ref>
|]
|-
!scope=row|March 16, 1896
|The dispute between the federal government, on behalf of ], and ] over ] was resolved in favor of the federal claim.<ref name="greer">{{ussc|162|1|1896}}</ref>
|]
|-
!scope=row|July 24, 1897
|To account for an earlier shift in the course of the ], an island was transferred from ] to ].<ref>{{usstat|30|214}}</ref>
|]
|}


==1898–1945 (Pacific and Caribbean expansion)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
The ] established the ] west of the ] as the border with British-held lands, and ] was established as a shared land between the United States and United Kingdom.
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change Map
|-
!scope=row|August 12, 1898
|The ] was annexed.<ref name="hawaii-annexed">{{cite web|url=https://history.state.gov/countries/hawaii |title=Hawaii |publisher=Office of the Historian, Bureau of Public Affairs, ] |access-date=May 14, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150619000455/http://history.state.gov/countries/hawaii |archive-date=June 19, 2015 }}</ref> The ceremony to transfer sovereignty occurred on this date; the ] was signed on July 7, 1898.<ref>{{USStat|30|750}}</ref> ] was not included with Hawaii, nor was ], which had been ceded to Hawaii in 1856 by its residents and approved by ]. However, the annexation was based on the islands named in a report of the Hawaiian Commission, which omitted Sikaiana.<ref> {{webarchive|url=https://web.archive.org/web/20080216015423/http://www.gao.gov/archive/1998/og98005.pdf |date=February 16, 2008 }} (pdf). Report to the Chairman, Committee on Resources, House of Representatives. ''United States General Accounting Office''. November 1997. Page 39, footnote 2.</ref><ref>Report of the Hawaiian Commission, S. Doc. No. 16, 55th Cong., at 4 (3d Sess. 1898)</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|January 17, 1899
|] was claimed.<ref>{{cite news|url=https://timesmachine.nytimes.com/timesmachine/1899/03/22/117916635.pdf |title=Wake Island Occupation |newspaper=] |date=March 21, 1899 |access-date=May 14, 2015 }}{{cbignore|bot=medic}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|April 11, 1899
|], ], and, on agreed payment of $20&nbsp;million, the ] were ] by ] following the ].<ref name="spanishamerican">{{cite web|url=http://avalon.law.yale.edu/19th_century/sp1898.asp |title=Treaty of Peace Between the United States and Spain; December 10, 1898 |publisher=The Avalon Project at Yale Law School |access-date=May 14, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150523121634/http://avalon.law.yale.edu/19th_century/sp1898.asp |archive-date=May 23, 2015 }}</ref> The Philippines were claimed by the ]. The ceded region for the Philippines included the island of ], which was administered by ]. This overlap would not be noticed until January 21, 1906.<ref name="palmas"/> While the United States occupied ] for a time, it was not ceded nor claimed.


|align="center"|Pacific Ocean:<br />]<br /><br />Caribbean Sea:<br />]
]
|-
;] ]
!scope=row|February 16, 1900
The southern portion of ] was admitted as the 21st state, ]. The remainder was added to ].
|The United States took ownership of the ] east of 171° west, per the terms of the ].<ref name="asbar"/>
{{-}}
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|February 19, 1900
|The newly acquired Samoan islands were established as ]. It included all of the islands granted by the ], though formal cession of the islands by local authorities would take place later in 1900 and 1904.<ref name="asbar"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|April 12, 1900
|] was ] into a civil territory.<ref>{{USStat|31|77}}</ref>
|align="center" rowspan=2|''no change to map''
|-
!scope=row|April 17, 1900
|The island of ] was ] to the United States and added to ].<ref name="asbar">{{cite web|url=http://www.asbar.org/archive/Newcode/treaties.htm |title=Treaties, Cessions, and Federal Laws |publisher=American Samoa Bar Association |access-date=May 11, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160304054025/http://www.asbar.org/archive/Newcode/treaties.htm |archive-date=March 4, 2016 }}</ref><ref>https://americansamoa.noaa.gov/about/history.html ''National Marine Sanctuary of American Samoa. History.'' americansamoa.noaa.gov. Retrieved January 18, 2018.</ref> As the United States had already claimed the island on February 19, 1900, no change is mapped. The ] by Congress on February 20, 1929.
|-
!scope=row|June 14, 1900
|The former ] was ] into ].<ref>{{USStat|31|141}}</ref><ref name="vz-hi">Van Zandt, p. 166</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|March 3, 1901
|The transfer for a thin sliver of ], to ], was approved by Congress after having been approved by both states.<ref>{{usstat|31|1465}}</ref><ref>Va. Code Ann. § 1-306, {{webarchive|url=https://web.archive.org/web/20160624063947/http://law.lis.virginia.gov/compacts/boundary-with-tennessee/ |date=June 24, 2016 }}</ref> The location of the border along Main Street (now State Street) between the two cities was either the northern sidewalk of the street, or down the middle of the street; Tennessee's cession of the northern half of the street laid the issue to rest.
|align="center"|''too small to map''
|-
!scope=row|March 23, 1901
|The president of the ], ], was captured, and the republic was dissolved.


On this same date several islands, ] and ] among them, were ] from ] and assigned to the Philippines, which was then being governed as a U.S. ]. The borders specified in the ] had excluded these islands; the new treaty simply ceded "any and all islands belonging to the Philippine Archipelago".<ref></ref><ref>{{usstat|31|1942}}</ref>
]
|align="center"|Pacific Ocean:<br />]
;] ]
|-
The unorganized land south of ] was organized as ].<ref name="statoids" /><!-- It was not officially spelled Arkansas until later -->
!scope=row|July 4, 1901
{{-}}
|The ] was established.<ref>{{cite web|url=https://history.house.gov/Exhibitions-and-Publications/APA/Historical-Essays/Exclusion-and-Empire/The-Philippines/ | title=The Philippines, 1898&mdash;1946|publisher=Office of the Historian of the United States House of Representatives | accessdate=January 25, 2022}}</ref><ref>{{usstat|31|895}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|July 1, 1902
|The ] were ].<ref>{{usstat|32|691}}</ref>
|align="center"|''no change to map''
|-
!scope=row|October 20, 1903
|The ] with ] was resolved, generally in favor of the United States claim.<ref name="vz-akboundary">Van Zandt, pp. 29–33</ref>
|align="center"|Northwestern North America:<br />]
|-
!scope=row|December 10, 1903
|Land along southern ] was ] in perpetuity from ] for use as a ];<ref>{{cite web
|url=http://avalon.law.yale.edu/20th_century/dip_cuba002.asp
|title=Agreement Between the United States and Cuba for the Lease of Lands for Coaling and Naval stations; February 23, 1903
|publisher=The Avalon Project at Yale Law School
|access-date=June 13, 2016
|url-status=live
|archive-url=https://web.archive.org/web/20160604195511/http://avalon.law.yale.edu/20th_century/dip_cuba002.asp
|archive-date=June 4, 2016
}}</ref> the treaty took effect February 23, 1903, and the formal handover occurred on this date.<ref>{{cite magazine | url=https://www.newyorker.com/news/news-desk/a-useful-corner-of-the-world-guantnamo | title=A Useful Corner of the World: Guantánamo | magazine=The New Yorker | date=July 30, 2013 | author=Kramer, Paul | access-date=June 4, 2018}}</ref>
|align="center"|''no change to map''
|-
!scope=row|May 4, 1904
|The United States took ownership of the ]. At this stage, only the most basic borders were defined; it was a zone surrounding the canal on each side for five miles, but excluded the cities of ] and ], which remained exclaves of ], as well as the water for their harbors.<ref>{{cite book|url=https://books.google.com/books?id=AYaaAAAAIAAJ&pg=PA133 |title=And the Mountains Will Move: The Story of the Building of the Panama Canal |author=DuVal, Miles P. |year=1947 |publisher=] |access-date=May 12, 2015 |isbn=978-0-8047-1151-7 |url-status=live |archive-url=https://web.archive.org/web/20160424143401/https://books.google.com/books?id=AYaaAAAAIAAJ&lpg=PR13&pg=PA133 |archive-date=April 24, 2016 }}</ref> The ] granting it to the United States was ratified on February 26, 1904.<ref>{{USStat|33|2234}}</ref> A formal border agreement, which also gave the Canal Zone some land and a lighthouse in northwest Colón, would be ratified on June 15, 1904.<ref> {{webarchive|url=https://web.archive.org/web/20160428195837/https://books.google.com/books?id=0UQ6AQAAIAAJ&lpg=PA678&ots=1Nl1z4L2jk&pg=PA678 |date=April 28, 2016 }}; signed June 15, 1904; accessed June 30, 2015</ref><ref name="vz-cz"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|July 16, 1904
|The ] islands were ] to the United States and added to ].<ref name="asbar"/> As the United States had already claimed the islands on February 19, 1900, no change is mapped. The ] by Congress on February 20, 1929.
|align="center" rowspan=2|''no change to map''
|-
!scope=row|December 12, 1904
|The "Taft Agreement" was made with ] on December 3, with one of its sections refining the maritime boundary of the harbor of ] and the ].<ref>{{cite book | title=Hearings concerning estimates for construction of the Isthmian Canal for the fiscal year 1909 | publisher=U.S. Government Printing Office | url=https://archive.org/details/hearingsconcern01tawngoog | page= | access-date=July 6, 2015| last1=Committee On Appropriations | first1=United States. Congress. House | last2=Tawney | first2=James A | year=1908 }}</ref><ref>H.R. Doc. No. 458 part 10, 58th Cong., 2nd Sess. (1904), pp. 936–941 (Specifically for this citation, )</ref> It became effective December 12.
|-
!scope=row|February 10, 1905
|The border between ] and ] was slightly adjusted near ], transferring a small amount of land on the east side of the ] to Arkansas.<ref>{{usstat|33|714}}</ref><ref>{{cite journal
|last1=Myers
|first1=Arther J.
|last2=Vosburg
|first2=David L.
|date=November 1964
|title=Distances Within the State of Oklahoma
|url=http://www.ogs.ou.edu/pubsscanned/NOTES/GN-V24N11.pdf
|journal=Oklahoma Geology Notes
|publisher=]
|volume=24
|issue=11
|pages=256
|access-date=May 17, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20160304192330/http://www.ogs.ou.edu/pubsscanned/NOTES/GN-V24N11.pdf
|archive-date=March 4, 2016
}}</ref>
|]
|-
!scope=row|September 26, 1907
|] became largely ] from the ],<ref></ref> inheriting the claim on the atolls of ], ], ], and ].
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|November 16, 1907
|] and ] were combined and admitted as the forty-sixth state, ].<ref name="vz-ok"/><ref>{{USStat|35|2160}}</ref>
|]
|-
!scope=row|April 11, 1908
|A boundary treaty with the ] on behalf of ] redefined the maritime borders between the United States and Canada.<ref>Van Zandt, pp. 18–20</ref> Among other changes, this "de-enclaved" ] in ] by making the water around it contiguous with the water on the American side of the border.<ref name="horseshoe"/><ref>{{cite map|url=https://www.scribd.com/doc/282773953/StLawrenceRiver-GreatLakes-12 |title=International Boundary between the United States and the Dominion of Canada through the St. Lawrence River and Great Lakes, Sheet No. 12 – Niagara River |publisher=International Waterways Commission |date=August 15, 1913 |access-date=August 8, 2016 |location=Buffalo, New York |url-status=live |archive-url=https://web.archive.org/web/20160304064348/https://www.scribd.com/doc/282773953/StLawrenceRiver-GreatLakes-12 |archive-date=March 4, 2016 }}</ref>
|align="center"|''no change to map''
|-
!scope=row|January 1, 1909
|The new ] included some area of ] within its definition of ].<ref name="wi-vs-mi"/>
|]
|-
!scope=row|August 20, 1910
|A boundary treaty with the ] on behalf of ] addressed a slight uncertainty in the maritime border in ] between ] and Canada.<ref></ref><ref>Van Zandt, p. 20</ref><ref name="maritime">{{cite web | url=https://2009-2017.state.gov/e/oes/ocns/opa/c28187.htm | title=Maritime Boundaries | publisher=United States Department of State | access-date=August 19, 2018}}</ref> The border was adjusted to run east of Pope's Folly Island, which previously lay on the border line, and had been the subject of some debate for many years.<ref>{{cite news|url=https://www.nytimes.com/1893/06/20/archives/who-owns-popes-folly-island-great-britains-original-chart-conceded.html |title=Who Owns Pope's Folly Island? |newspaper=] |date=June 20, 1893 |access-date=May 11, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160305202433/http://query.nytimes.com/gst/abstract.html?res=950CE6DE163EEF33A25753C2A9609C94629ED7CF |archive-date=March 5, 2016 }}</ref><ref>Link to a download for the ] map of the Eastport Quadrangle from 1907: </ref>
|]
|-
!scope=row|July 17, 1911
|Naval Station, Tutuila, was renamed ];<ref>{{cite news|url=http://www.samoanews.com/viewstory.php?storyid=7779 |archive-url=https://archive.today/20110927012532/http://www.samoanews.com/viewstory.php?storyid=7779 |archive-date=September 27, 2011 |access-date=May 11, 2015 |date=July 16, 2009 |title=Manu'a celebrates 105 years under the U.S. Flag |publisher=] |url-status=dead }}</ref> the station ] separate from territorial governance until 1951.
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|January 6, 1912
|] was admitted as the forty-seventh state, ].<ref name="vz-nm"/><ref>{{usstat|37|39}}</ref>
|]
|-
!scope=row|February 14, 1912
|] was admitted as the forty-eighth state, ].<ref name="vz-az"/><ref>{{usstat|37|1728}}</ref>
|]
|-
!scope=row|August 24, 1912
|The ] was reorganized as the ].<ref>{{USStat|37|512}}</ref>
|align="center"|Northwestern North America:<br />]
|-
!scope=row|January 31, 1913
|New Mexico filed suit in the ] against ] over the "]", questioning whether the present course or the 1850 course of the ] should be their border.<ref>{{cite journal
|last = Bowden
|first = J.J.
|date = October 1959
|title = The Texas-New Mexico Boundary Dispute Along the Rio Grande
|url = http://faculty.utep.edu/LinkClick.aspx?link=Bowden_NM-TX+boundary.pdf&tabid=72958&mid=166250
|journal = ]
|publisher = ]
|volume = 63
|issue = 2
|pages = 221–237
|access-date = May 11, 2015
|archive-url = https://web.archive.org/web/20160304035215/http://faculty.utep.edu/LinkClick.aspx?link=Bowden_NM-TX+boundary.pdf&tabid=72958&mid=166250
|archive-date = March 4, 2016
|url-status = dead
}}</ref>
|]
|-
!scope=row|August 5, 1914
|The ] were ] from ] for a period of ]; however, this was not a full transfer of sovereignty, and the islands were never administered as an insular area.<ref name="doi-former"/>
|align="center"|''no change to map''
|-
!scope=row|May 1, 1915
|The borders of the ] were explicitly defined. Whereas the original definition was a simple corridor surrounding the canal, this treaty specified the actual border. Among the changes this caused were: a slice of Canal Zone was ceded to ] so ] would be connected with the rest of the country; the middle island of the Las Tres Hermanas Islands, which marked the border of Panama City's harbor, was wholly made part of Canal Zone; ] and other surrounding waters were formally annexed to the territory; and an area of northwest ] was ceded to Canal Zone.<ref>{{usstat|38|1893}}</ref><ref> {{webarchive|url=https://web.archive.org/web/20160516113457/https://books.google.com/books?id=0UQ6AQAAIAAJ&ots=1Nl-C4G1ko&pg=PA702 |date=May 16, 2016 }}, signed September 2, 1914; U.S. Treaty Series 610; accessed June 30, 2015</ref><ref>{{cite news|title=Boundary Convention |date=June 9, 1915 |newspaper=The Canal Record |location=] |access-date=June 30, 2015 |url=https://www.newspapers.com/image/50612129 |url-status=live |archive-url=https://web.archive.org/web/20160827105545/http://www.newspapers.com/image/50612129/ |archive-date=August 27, 2016 }}</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|May 27, 1915
|Under Article II of the ], the United States expropriated from ] several areas around the mouth of the ], annexing them to the ].<ref name="McCain">{{cite book| title=The United States and the Republic of Panama (2nd printing) |first=William D. |last=McCain| location= New York |publisher=Russell & Russell |year=1965 |
pages=144–159}}</ref>
|align="center" rowspan=2|''too small to map''
|-
!scope=row|December 8, 1915
|The United States expropriated from ] a triangle of land, which included the historic ], between the ], ] and the ], to which it was annexed.<ref name="McCain"/>
|-
!scope=row|January 17, 1916
|] was formally claimed for lighthouse purposes.<ref>{{usstat|39|1763}}</ref>
|align="center" rowspan=2|''no change to map''
|-
!scope=row|August 29, 1916
|The ] were ] to provide more autonomous government.<ref>{{usstat|39|545}}</ref>
|-
!scope=row|March 31, 1917
|The ] were ] from ]<ref>{{USStat|39|1706}}</ref> and renamed the ].<ref name="vz-vi">Van Zandt, pp. 39–40</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|July 12, 1918
|The United States expropriated from ] 2.6 hectares of land at ] in ] and annexed it to the ].<ref>{{cite journal|location=Panama|publisher=Republic of Panama|title=Letter, Chester Harding (Governor of the Panama Canal Zone) to Luis Urriola (President of the Republic of Panama), July 12, 1918|pages=303–305|journal=Memoria Que Presenta el Secretario de Relaciones Exteriores a la Honorable Asamblea Nacional en Sus Sesiones Ordinarias de 1918|year=1919|url=https://babel.hathitrust.org/cgi/pt?id=njp.32101058620723;view=1up;seq=6}}</ref> That area was enlarged to about 50 hectares within several months.<ref name="McCain"/><ref>{{cite news|title= The Panama Canal Record |publisher= The Panama Canal |pages=584–585 |volume=XIII |number=39|location= Balboa Heights, Canal Zone |date=May 12, 1920 |url=http://www.ebooksread.com/dl2.php?action=prepare_file&id=250463&ext=pdf_external&f=panamacanalr13191920isth&a_id=97730 |quote=...&nbsp;it was not until the year 1918, when the Governor of the Canal Zone addressed a communication to the Secretary of Foreign Affairs of the Republic of Panama stating that the United States Government would require 50.6 hectares, that the exact area expropriated was definitely known.}}</ref><ref>{{cite book|title=Annual Report of the Governor of the Panama Canal for the Fiscal Year ended June 30, 1919 |url=https://archive.org/details/annualreportofgo1919cana |last=Canal Zone. Office of the Governor. |publisher=U.S. Government Printing Office |year=1919 |location=Washington, DC |page= |quote=A survey was made and a map drawn up showing the boundary lines of the Punta Paitilla military reservation. Various areas were determined with reference to high and low water and the old and new city boundary lines. Permanent monuments were set and a description written up by metes and bounds. A tracing was made of the map of the military reservation known as area 'A'. |url-status=live |archive-url=https://web.archive.org/web/20160506134624/https://archive.org/details/annualreportofgo1919cana |archive-date=May 6, 2016 }}</ref><ref name="CZmap">{{cite map|title=Panama Canal Zone and Vicinity Showing Judicial Districts |publisher=United States Army |location=National Archives, College Park, Maryland |url=https://catalog.archives.gov/id/6861831?q=map%2520panama%2520canal |date=1927 |url-status=live |archive-url=https://web.archive.org/web/20161011034402/https://catalog.archives.gov/id/6861831?q=map%20panama%20canal |archive-date=October 11, 2016 }} (with hand-drawn features dated 1932)</ref>
|align="center"|''too small to map''
|-
!scope=row|August 21, 1918
|The United States expropriated from ] land between the ] and the and annexed it to the ].<ref name="McCain"/><ref name="CZmap"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|September 13, 1918
|] and ] exchanged islands in the ]: Island Seventytwo was transferred to ], and Barron's Island was transferred to ].<ref name="vz-wi"/><ref>{{usstat|40|959}}</ref>
|]
|-
!scope=row|September 18, 1919
|The island of Largo Remo was annexed to the ] under the United States right of expropriation in the 1903 Canal Treaty.<ref>U.S. For. Rel., 1920, III, 314–322; Specifically, </ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|June 16, 1920
|Fifteen hectares on the island of ] were annexed to the ].<ref>U.S. For. Rel., 1920, III, 314–322; Specifically, </ref>
|align="center"|''too small to map''
|-
!scope=row|June 30, 1921
|The "]" dispute between ] and ] was resolved in Delaware's favor. The disputed land had generally been administered by Delaware, even electing a member of the Delaware legislature in the mid-19th century,<ref name="walkin-the-line">{{cite book|title=Walkin' the Line: A Journey from Past to Present Along the Mason-Dixon |author=Ecenbarger, Bill |date=August 30, 2001 |publisher=M. Evans and Company, Inc. |url=https://books.google.com/books?id=6LfAGeUd5z4C&pg=PA90 |pages=89–91 |access-date=May 10, 2015 |isbn=978-1-4617-1076-9 |url-status=live |archive-url=https://web.archive.org/web/20160423134203/https://books.google.com/books?id=6LfAGeUd5z4C&lpg=PA91&pg=PA90 |archive-date=April 23, 2016 }}</ref> but federal maps had included the land as part of Pennsylvania at least as late as 1900.<ref>Link to a download for the ] map of the Elkton Quadrangle from August 1900: . Note that later reprints of the same map, as early as 1906, changed ownership of the Wedge to Delaware: </ref> The states had agreed on a resolution, and it was affirmed by an act of Congress on this date.<ref>{{cite web|url=https://books.google.com/books?id=1S8PAAAAYAAJ&pg=PA104 |title=Pub.Res. 7 |year=1921 |url-status=live |archive-url=https://web.archive.org/web/20160409083458/https://books.google.com/books?id=1S8PAAAAYAAJ&lpg=PR6&ots=VKqZWgDpgf&pg=PA104 |archive-date=April 9, 2016 |last1=States |first1=United }}</ref><ref name="delaware-curve">{{cite journal
| last = Hayes
| first = J. Carroll
| date = July 1923
| title = The Delaware Curve: The Story of the Pennsylvania-Delaware Circular Boundary
| url = https://journals.psu.edu/pmhb/article/viewFile/27979/27735
| journal = ]
| publisher = ]
| volume = 47
| issue = 3
| access-date = May 10, 2015
}}</ref> Some sources, both contemporary and modern, note that, in the original process of resurveying the border in 1892, a very thin, horn-shaped region along the arc was transferred from Delaware to Pennsylvania;<ref name="walkin-the-line"/><ref name="delaware-curve"/><ref>{{cite news|url=https://www.nytimes.com/1892/12/19/archives/refuse-to-be-expatriated-citizens-of-drlaware-decline-to-become.html |title=Refuse to be Expatriated: Citizens of Delaware Decline to Become Pennsylvanians |date=December 19, 1892 |newspaper=] |access-date=May 10, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160305002733/http://query.nytimes.com/gst/abstract.html?res=9F07E1DB1F31E033A2575AC1A9649D94639ED7CF |archive-date=March 5, 2016 }}</ref> however, no federal maps found reflect this, and it is unclear if this transfer actually occurred.
|]
|-
!scope=row|May 10, 1922
|] was formally annexed.<ref name="doi-kingman">{{cite web|url=https://www.doi.gov/oia/islands/kingmanreef |publisher=] |title=Kingman Reef |date=12 June 2015 |access-date=July 15, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160815122443/https://www.doi.gov/oia/islands/kingmanreef |archive-date=August 15, 2016 }}</ref>
|align="center"|''no change to map''
|-
!scope=row|October 8, 1923
|] expanded its claim to ] territory, though Wisconsin never lost control over the area.<ref name="wi-vs-mi"/>
|]
|-
!scope=row|November 15, 1923
|The ] were claimed by ].<ref> {{webarchive|url=https://web.archive.org/web/20160304064239/http://images.library.wisc.edu/FRUS/EFacs/1940v05/reference/frus.frus1940v05.i0016.pdf |date=March 4, 2016 }}, accessed July 8, 2015</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|February 1, 1924
|The future area for ] was annexed to the ] under the United States right of expropriation in the 1903 Canal Treaty.<ref name="vz-cz">Van Zandt, pp. 58–60</ref><ref>{{cite book|title=Annual Report of the Governor of the Panama Canal for the Fiscal Year ended June 30, 1924 |page=|location=Washington, DC|publisher= Government Printing Office|year=1924|url=https://archive.org/details/annualreportofgo1924cana|access-date=July 10, 2016}}</ref><ref>{{cite executive order | number = 4019 | url = https://books.google.com/books?id=4cE-AAAAIAAJ&pg=PA336 | date = June 5, 1924 | language = English | post = President of the United States | access-date = June 30, 2015}}</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|March 4, 1925
|] was added to ].<ref>{{cite web |url=http://legisworks.org/congress/68/pubres-75.pdf |title=Pub.Res. 75 |year=1925 |url-status=dead |archive-url=https://web.archive.org/web/20151030103928/http://legisworks.org/congress/68/pubres-75.pdf |archive-date=October 30, 2015 |access-date=July 1, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|July 17, 1925
|The border with ] was adjusted in several places.<ref>{{cite web |url=http://treaties.fco.gov.uk/docs/pdf/1925/TS0037.pdf |title=Treaty Between Canada and the United States of America to define more accurately and to complete the International Boundary between the two Countries |date=February 24, 1925 |access-date=May 8, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20160816222704/http://treaties.fco.gov.uk/docs/pdf/1925/TS0037.pdf |archive-date=August 16, 2016 }}</ref><ref>Van Zandt, pp. 21–22</ref> The only change to a land border redefined how the border between the ] and the ] should be considered; previously, the border followed the curve of the parallel between each border monument, while the treaty changed this to straight lines between each monument. Through this, the United States netted a gain of between 30 and 35 acres of land. Because of the extremely small shift, the lack of specific documentation of where the changes occurred, and the lack of any human impact, this change is not mapped. There was also a change to the border in the ]; a surveying anomaly caused the previous border to intersect itself several times in the lake, creating enclaves of United States water surrounded by Canadian water. The treaty changed the border to use the southernmost intersection as the ]. Finally, the maritime border in the ] was adjusted, netting Canada roughly 9 acres of water.
|align="center"|''too small to map''
|-
!scope=row|March 1, 1926
|The ] resolved the conflict between ] and ] in the favor of ].<ref name="wi-vs-mi">{{ussc|name=Wisconsin v. Michigan|volume=270|page=295|year=1926}}</ref>
|]
|-
!scope=row|July 29, 1926
|] was established as a federal bird refuge and placed under the jurisdiction of the ].<ref>{{cite executive order |number=4467 |date=July 26, 1926 |language=English |post=President of the United States}}</ref> The atoll had originally been claimed by both the United States and Hawaii in 1858, but little activity apart from guano mining had taken place, and it had been largely abandoned for decades.<ref name="doi-johnston">{{cite web | url=http://elips.doi.gov/ELIPS/0/doc/1771/Page5.aspx | title=Departmental Manual | publisher=] ] | access-date=July 15, 2016 }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
|align="center"|''no change to map''
|-
!scope=row|November 22, 1926
|The ] defined the border between ] and ], transferring all islands south of the Quinnesec Falls on the ] to Wisconsin, and all islands north of the falls to ]; it is unknown specifically which islands were transferred in this fashion. However, an error in the border description introduced a small overlap between the two states over several islands in ] north of the ].<ref>{{ussc|name=Wisconsin v. Michigan|volume=272|page=398|year=1926}}</ref>
|]
|-
!scope=row|July 18, 1927
|The United States expropriated from ] another 33 hectares of land on the islands of ] and Taboguilla and annexed them to the ].<ref name="McCain"/>
|align="center" rowspan=2|''too small to map''
|-
!scope=row|October 26, 1927
|Two ] along the ] were ceded from ] to ].<ref>{{cite web|url=http://www.ibwc.gov/Files/Minutes/Min99.pdf |title=Minute 99: Re accretions lands on Colorado River—also Farmers and Fain Bancos.Decision reached. |publisher=] |date=October 26, 1927 |access-date=January 12, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160304132221/http://www.ibwc.gov/Files/Minutes/Min99.pdf |archive-date=March 4, 2016 }}</ref><ref name="bancos">{{cite web|url=http://www.ibwc.state.gov/Treaties_Minutes/Minutes.html |title=Minutes between the United States and Mexican Sections of the IBWC |publisher=] |access-date=January 6, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20150713015418/http://www.ibwc.state.gov/Treaties_Minutes/Minutes.html |archive-date=July 13, 2015 }}</ref>
|-
!scope=row|December 5, 1927
|The "]" between ] and ] was resolved in Texas's favor.<ref>{{ussc|name=New Mexico v. Texas|volume=275|page=279|year=1927}}</ref>
|]
|-
!scope=row|April 4, 1928
|The ] was decided in the favor of ], ceding ] to the ].<ref name="palmas"> {{webarchive|url=https://web.archive.org/web/20161003090103/http://legal.un.org/riaa/cases/vol_II/829-871.pdf |date=October 3, 2016 }}, April 4, 1928; accessed June 2, 2015</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|September 24, 1928
|The United States expropriated from ] three hectares of land at ''El Cerro de Doscientos Pies'' ("200-Foot Hill") near Las Minas Bay and annexed it to the ].<ref name="McCain"/><ref name="CZmap"/>
|align="center" rowspan=2|''too small to map''
|-
!scope=row|July 22, 1930
|The United States expropriated from ] 25 hectares on Jicarita Island and 60 hectares at Punta Morro de Puercos and annexed them to the ].<ref name="McCain"/>
|-
!scope=row|April 15, 1931
|The United States expropriated from ] additional areas around the soon-to-be-built ] and annexed them to the ].<ref name="McCain"/><ref name="CZmap"/>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|May 3, 1932
|The United States adjusted the border at ] in the Canal Zone, returning a small amount of land to ]. This was the site for a planned new American embassy, which had to be built on foreign soil.<ref>{{usstat|47|145}}</ref>
|align="center"|''too small to map''
|-
!scope=row|May 17, 1932
|Porto Rico was renamed ].<ref>{{UnitedStatesCode2|48|731a|Change of name; Puerto Rico}}</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|December 13, 1932
|The Mangsee Islands and seven of the ] were ] by the ] from ] to the ]. The islands were supposed to be included in the 1900 transfer of islands from ] to the United States. Per the terms of the treaty, the United Kingdom continued to administer the islands until requested, and, after the Philippines' independence, the Philippine government made such a request and took control.<ref>{{usstat|47|2198}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|May 29, 1933
|The ] ] that the border between ] and ] was the low water mark of the west bank of the ]; Vermont had sought to have the border placed in the middle of the river.<ref name="ReferenceA"/>
|align="center"|''no change to map''
|-
!scope=row|November 13, 1933
|A treaty created the ], which, from 1935 to 1938, straightened and stabilized the path of the ] through the ]–] Valley. By the end of the project, 174 parcels had been transferred between ] and ], each side receiving an equal area of land.<ref>{{cite book | url=https://books.google.com/books?id=_5RQooKRgY0C | page=1027 | title=American Water Resources Administration | access-date=June 22, 2016| last1=Shih | first1=Yang-Ch'Eng }}</ref><ref>The details of the project are contained in IBWC minutes 145 through 167.{{cite web|url=http://www.ibwc.state.gov/Treaties_Minutes/Min_1_179.htm |title=Minutes 1 through 179 |publisher=] |access-date=June 22, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20150616033532/http://www.ibwc.state.gov/Treaties_Minutes/Min_1_179.htm |archive-date=June 16, 2015 }}</ref>
|align="center"|''too small to map''
|-
!scope=row|December 29, 1934
|] was placed under the jurisdiction of the ].<ref name="doi-kingman"/>
|align="center"|''no change to map''
|-
!scope=row|November 15, 1935
|The ] was ] with the ].<ref>{{cite web | url=https://www.lawphil.net/executive/proc/proc1935/proc_2148_1935.html | title=Proclamation 2148&mdash;Establishment of the Commonwealth of the Philippines | publisher=The American Presidency Project | accessdate=January 25, 2022 | archive-date=January 25, 2022 | archive-url=https://web.archive.org/web/20220125170409/https://www.lawphil.net/executive/proc/proc1935/proc_2148_1935.html | url-status=dead }}</ref><ref>{{usstat|48|456}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|March 16, 1936
|The de jure overlap between ] and ] was ] by the ].<ref>{{ussc|name=Wisconsin v. Michigan|volume=297|page=547|year=1936}}</ref>
|]
|-
!scope=row|May 13, 1936
|], ], and ] were formally annexed and placed under the jurisdiction of the ],<ref>{{cite executive order |number=7368|date=May 13, 1936|language=English |post=President of the United States}}</ref> ending the ]'s claim to Jarvis Island.<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|June 22, 1936
|The ] were ] into a civil territory.<ref>{{usstat|49|1807}}</ref>
|align="center"|''no change to map''
|-
!scope=row|August 6, 1936
|], ], and ] were claimed by the ].<ref name="uk-chrono"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|April 6, 1939
|The condominium of the ] was established with the ].<ref>{{cite book | url=https://books.google.com/books?id=yc8WAAAAYAAJ&pg=PA543 | title=Treaties and Other International Agreements of the United States, Volume 12 | access-date=April 12, 2015| last1=Bevans | first1=Charles Irving | year=1976 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|July 27, 1939
|] gained a sovereign corridor that was carved out of the ] connecting ] with the rest of ], along with a three-dimensional "tube" of sovereignty for a future crossing over an American highway. A corridor consisting of the road from the Canal Zone boundary to ] was annexed to the Canal Zone.<ref>{{cite web|url=https://www.loc.gov/law/help/us-treaties/bevans/b-pa-ust000010-0742.pdf |title=Treaty of Friendship and Cooperation |publisher=Library of Congress |access-date=November 2, 2016 |url-status=live |archive-url=https://web.archive.org/web/20161104004354/https://www.loc.gov/law/help/us-treaties/bevans/b-pa-ust000010-0742.pdf |archive-date=November 4, 2016 }}</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|August 16, 1939
|This is the earliest date so far discovered for when the United States began claiming ], ], ], ], ], and ].<ref>{{cite book|title=Foreign relations of the United States diplomatic papers, General, the British Commonwealth and Europe (1939) |publisher=] |year=1939 |pages=317–319 |url=http://digicoll.library.wisc.edu/cgi-bin/FRUS/FRUS-idx?type=turn&entity=FRUS.FRUS1939v02.p0326&id=FRUS.FRUS1939v02&isize=M |url-status=live |archive-url=https://web.archive.org/web/20160304110645/http://digicoll.library.wisc.edu/cgi-bin/FRUS/FRUS-idx?type=turn&entity=FRUS.FRUS1939v02.p0326&id=FRUS.FRUS1939v02&isize=M |archive-date=March 4, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|December 10, 1941
|Governor ] surrendered ] to the ] military.<ref name="guam-ww2">{{cite web|url=http://www.guampedia.com/japanese-occupation-of-guam/ |title=Japanese Occupation of Guam |date=October 2009 |publisher=Guampedia |access-date=April 12, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150402230108/http://www.guampedia.com/japanese-occupation-of-guam/ |archive-date=April 2, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|December 23, 1941
|The garrison on ] surrendered to the ] military.<ref name="wake-ww2"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|March 26, 1942
|The government of the ] evacuated from the territory in the face of ] advance. A ] would be established in ], on May 17, 1942. The ] would surrender on April 9, 1942, following the ], and the final military holdouts would surrender on May 6, 1942, following the ].<ref name="philippines-ww2"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|October 14, 1943
|The ] was established as a ] of ].<ref name="philippines-ww2"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|August 10, 1944
|] was ] from ].<ref name="guam-ww2"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|August 17, 1945
|The ], in exile in ] since April 3, 1945, was dissolved. The process of re-establishing the Commonwealth government on Philippine soil had started on October 23, 1944.<ref name="philippines-ww2">{{cite web|url=http://malacanang.gov.ph/5235-70th-anniversary-of-the-second-philippine-republic/ |title=71st Anniversary of the Second Philippine Republic |publisher=Republic of the Philippines Presidential Museum and Library |access-date=April 11, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150315013844/http://malacanang.gov.ph/5235-70th-anniversary-of-the-second-philippine-republic/ |archive-date=March 15, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|September 4, 1945
|The ] garrison on ] surrendered to the United States.<ref name="wake-ww2">{{cite web|url=http://www.history.navy.mil/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-96000/NH-96813.html |title=Surrender of Wake Atoll, 4 September 1945 |publisher=] |access-date=April 11, 2015 |url-status=live |archive-url=https://web.archive.org/web/20161023112636/https://www.history.navy.mil/our-collections/photography/numerical-list-of-images/nhhc-series/nh-series/NH-96000/NH-96813.html |archive-date=October 23, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|}


==1946–present (Decolonization)==
]
{|class="wikitable plainrowheaders"
;] ]
|-
] was admitted as the 22nd state, ].
!scope="col"|Date
{{-}}
!scope="col"|Event
!scope="col"|Change map
|-
!scope=row|July 4, 1946
|The ] ] as the ].<ref name="phil-independence">{{cite web|url=https://treaties.un.org/doc/Publication/UNTS/Volume%207/v7.pdf |title=United Nations Treaty Series Volume 7 |access-date=April 10, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150924110851/https://treaties.un.org/doc/Publication/UNTS/Volume%207/v7.pdf |archive-date=September 24, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|July 18, 1947
|The ] entrusted the ] to the United States.<ref name="ttpi">{{cite executive order |number=11021 |url=https://www.archives.gov/federal-register/codification/executive-order/11021.html |date=July 1, 1962 |language=English |post=President of the United States |access-date=April 10, 2015}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|January 1, 1949
|The ] were incorporated into ], which inherited the claims on ], ], and ].<ref> {{webarchive|url=https://web.archive.org/web/20160816132843/http://www.legislation.govt.nz/act/public/1948/0024/1.0/DLM247577.html |date=August 16, 2016 }}, NZ Pub Act 1948 No. 24; accessed July 2, 2015</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|August 1, 1950
|] was ] into a civil territory.<ref>{{cite web|url=http://www.guampedia.com/organic-act-of-guam/ |title=Organic Act of Guam |date=3 September 2013 |publisher=Guampedia |access-date=June 30, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150402225954/http://www.guampedia.com/organic-act-of-guam/ |archive-date=April 2, 2015 }}</ref><ref>{{usstat|64|384}}</ref>
|align="center"|''no change to map''
|-
!scope=row|August 3, 1950
|] and ] exchanged small portions of land along the ], to accord with shifts in the river following a flood in 1944.<ref>{{usstat|64|397}}</ref>
|]
|-
!scope=row|May 6, 1954
|] and ] defined their border around the mouth of the ].<ref>{{usstat|68|77}}</ref><ref>{{Cite web |last=Klinga |first=Emily |title=History of Perdido Key |url=https://visitperdido.com/history-of-perdido-key |access-date=2024-10-30 |website=Visit Perdido Key | publisher=Perdido Key Chamber of Commerce |language=en-US}}</ref>
|align="center"|''not mapped''
|-
!scope=row|April 11, 1955
|Panama's corridor connecting ] with the rest of ] was realigned within the ]. Several three-dimensional "tubes" of sovereignty were also created, allowing Panamanian bridges to pass over rivers and a highway at several locations within the Canal Zone.<ref> {{webarchive|url=https://web.archive.org/web/20160304125242/https://treaties.un.org/doc/Publication/UNTS/Volume%20241/v241.pdf |date=March 4, 2016 }}, signed May 24, 1950; ] 3430; accessed June 30, 2015</ref><ref>{{cite book|first=Evgeny| last=Vinokurov| title = Theory of Enclaves | year = 2007| publisher = Lexington Books, Lanham, MD|pages=190–192| url= https://books.google.com/books?id=DcixBgtKMwUC&pg=PA190|access-date=June 30, 2015| isbn=978-0-7391-2403-1}}</ref>
|align="center"|''too small to map''
|-
!scope=row|August 23, 1955
|Several border locations of the ] were redefined. Punta Paitilla, the land held on ], and the remaining American holdings in ] and ] were ceded to ].<ref name="vz-cz"/><ref> {{webarchive|url=https://web.archive.org/web/20160821201656/https://treaties.un.org/doc/Publication/UNTS/Volume%20243/v243.pdf |date=August 21, 2016 }}, signed January 25, 1955; ] 3454; accessed June 30, 2015</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|January 3, 1959
|The ] was admitted as the forty-ninth state, ].<ref name="vz-ak"/>
|align="center"|Northwestern North America:<br />]
|-
!scope=row|August 21, 1959
|Most of ] was admitted as the fiftieth state, ]. ] was excluded from statehood and remained a territory.<ref name="doi-palmyra"/><ref name="vz-hi"/>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|August 25, 1961
|About 20 acres of land was transferred from ] to ] near ].<ref name="vz-mn"/><ref>{{usstat|75|399}}</ref>
|align="center"|''too small to map''
|-
!scope=row|January 14, 1964
|The ], a tract of land between ], and ], was divided between the United States and ].<ref>{{cite web|url=http://www.ibwc.gov/Files/ChamizalConvention1963.pdf |title=Boundary: Solution of the Problem of the Chamizal |date=August 29, 1963 |access-date=April 9, 2015 |publisher=] |url-status=live |archive-url=https://web.archive.org/web/20141219222000/http://www.ibwc.gov/Files/ChamizalConvention1963.pdf |archive-date=December 19, 2014 }}</ref>
|]
|-
!scope=row|August 4, 1965
|The ] became self-governing from ]. It claimed the atolls of ], ], ], and ].<ref>{{cite web |url=http://www.parliament.gov.ck/Constitution.pdf |title=Constitution of the Cook Islands |access-date=July 2, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150924064410/http://www.parliament.gov.ck/Constitution.pdf |archive-date=September 24, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|December 30, 1966
|Land on ] in the ] was leased from the ] for use as a military base.<ref>Van Zandt p. 43</ref>
|align="center" rowspan=2|''no change to map''
|-
!scope=row|April 25, 1971
|The lease of the ] from ] was terminated.<ref name="doi-former"/>
|-
!scope=row|September 1, 1972
|The United States recognized the sovereignty of Honduras over the ].<ref name="doi-former"/><ref>{{cite web
|url=https://treaties.un.org/doc/Publication/UNTS/Volume%20851/volume-851-I-12199-English.pdf
|title=Treaty on the Swan Islands
|access-date=June 17, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20160821215204/https://treaties.un.org/doc/Publication/UNTS/Volume%20851/volume-851-I-12199-English.pdf
|archive-date=August 21, 2016
}}</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|March 1, 1977
|The United States ] maritime borders west of the ], within the ], and in the ] that conflicted with claims of ].<ref name="IBRU">{{cite web|url= http://www.dur.ac.uk/resources/ibru/publications/full/bsb5-3_gray.pdf |title=Canada's Unresolved Maritime Boundaries|pages=61–67|last=Gray|first=David H.| work= IBRU Boundary and Security Bulletin|date=Autumn 1997|access-date=March 21, 2015}}</ref>
|align="center"|''no change to map''
|-
!scope=row|May 26, 1977
|Several parcels were ] between ] and ] along the ] in areas near ] and ],<ref>{{cite web|url=http://www.ibwc.gov/Treaties_Minutes/Minutes.html |title=Minutes between the United States and Mexican Sections of the IBWC |publisher=International Boundary and Water Commission |quote=Approvals: United States – May 26, 1977 Mexico – May 26, 1977 |url-status=live |archive-url=https://web.archive.org/web/20161118085558/http://www.ibwc.gov/Treaties_Minutes/Minutes.html |archive-date=November 18, 2016 }}</ref> including the ], on which the town of ] was located,<ref>{{cite web|date=September 26, 1987 |url=https://www.nytimes.com/1987/09/26/world/south-of-border-was-once-north.html |title=South of Border Was Once North |work=] |access-date=November 11, 2013 |last=Rohter, Larry |url-status=live |archive-url=https://web.archive.org/web/20140309094658/http://www.nytimes.com/1987/09/26/world/south-of-border-was-once-north.html |archive-date=March 9, 2014 }}</ref> and Beaver Island near ]. In addition, Mexico ceded {{convert|823|acre|km2}} to the U.S., while the U.S. ceded {{convert|2177|acre|km2}} to Mexico, primarily to straighten sections of the Rio Grande for flood control.<ref>{{cite web|url=https://www.ibwc.gov/Files/Minutes/Min257.pdf|title=Completion of the Relocations of the Rio Grande Stipulated in Article I of the Treaty of November 23, 1970 (Minute No. 257)|publisher=]|date=May 18, 1977|access-date=April 9, 2015|archive-date=April 7, 2016|archive-url=https://web.archive.org/web/20160407100030/http://www.ibwc.gov/Files/Minutes/Min257.pdf|url-status=dead}}</ref>
|]
|-
!scope=row|December 16, 1977
|A ] defining the maritime border with ] was signed; though it has never been ratified by the ], it is provisionally enforced by agreement renewed every two years.<ref name="maritime"/>
|align="center"|''no change to map''
|-
!scope=row|October 1, 1978
|] became independent from the ]. It claimed the atolls of ], ], ], and ].<ref>{{cite web|url=http://www.paclii.org/tv/legis/consol_act/cot277/ |title=Constitution of Tuvalu |access-date=July 2, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150828063609/http://www.paclii.org/tv/legis/consol_act/cot277/ |archive-date=August 28, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|July 12, 1979
|The ] became independent from the ]. It claimed ], ], ], ], ], ], ], ], ], ], ], ], ], and ]. This dissolved the condominium of the ].<ref>{{cite web|url=http://www.parliament.gov.ki/content/constitution-kiribati |title=Constitution of Kiribati |year=1979 |access-date=April 9, 2015 |publisher=Government of Kiribati |url-status=dead |archive-url=https://web.archive.org/web/20150921142232/http://www.parliament.gov.ki/content/constitution-kiribati |archive-date=September 21, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|October 1, 1979
|The ] was ] to ]. The United States and Panama continued to share operational control of the canal until December 31, 1999, when it would be fully turned over to Panama.<ref name="torrijos-carter">{{cite web|url=https://history.state.gov/milestones/1977-1980/panama-canal |publisher=] |date=October 31, 2013 |access-date=April 9, 2015 |title=The Panama Canal and the Torrijos-Carter Treaties |url-status=live |archive-url=https://web.archive.org/web/20141108144121/https://history.state.gov/milestones/1977-1980/panama-canal |archive-date=November 8, 2014 }}</ref> The United States retained control over several hundred specified areas to be turned over in ] over the years.
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|November 24, 1980
|The maritime border between the United States and ] was defined.<ref name="maritime"/><ref> {{webarchive|url=https://web.archive.org/web/20160304204522/https://treaties.un.org/doc/Publication/UNTS/Volume%201273/v1273.pdf |date=March 4, 2016 }}, signed March 28, 1978; ] 20984; accessed June 30, 2015</ref>
|align="center"|''no change to map''
|-
!scope=row|September 17, 1981
|The United States recognized the sovereignty of ] over ] and ], and the claim on ] was abandoned by the United States, as it was no longer above the seas at high tide, and thus the government considered it unclaimable.<ref name="doi-former"/><ref>{{cite web
|url=https://treaties.un.org/doc/Publication/UNTS/Volume%201307/volume-1307-I-21801-English.pdf
|title=Treaty between the Government of the United States of America and the Government of the Republic of Colombia Concerning the Status of Quita Sueño, Roncador, and Serrana
|access-date=June 17, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20160304073205/https://treaties.un.org/doc/Publication/UNTS/Volume%201307/volume-1307-I-21801-English.pdf
|archive-date=March 4, 2016
}}</ref>
|align="center"|Caribbean Sea:<br />]
|-
!scope=row|September 3, 1983
|The United States ] of the ] territory of ] over ], ], and ], and defined the maritime border with Tokelau.<ref name="maritime"/><ref name="doi-former"/><ref>{{cite web
|url=https://treaties.un.org/doc/Publication/UNTS/Volume%201643/v1643.pdf
|title=Treaty between the United States of America and New Zealand on the Delimitation of the Maritime Boundary between Tokelau and the United States of America
|pages=251–267
|access-date=June 17, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20160304230003/https://treaties.un.org/doc/Publication/UNTS/Volume%201643/v1643.pdf
|archive-date=March 4, 2016
}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|September 8, 1983
|The United States ] of the ] over ], ], ], and ], and the maritime border with the Cook Islands was defined.<ref name="maritime"/><ref name="doi-former"/><ref>
{{cite web|url=https://2009-2017.state.gov/documents/organization/125388.pdf |title=Treaty between the United States of America and the Cook Islands |date=June 11, 1980 |access-date=April 8, 2015 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|September 23, 1983
|The United States ] of ] over ], ], ], ], ], ], ], ], ], ], ], ], ], and ].<ref name="doi-former">{{cite web|url=https://www.doi.gov/oia/islands/disputedislands |title=Formerly Disputed Islands |date=12 June 2015 |publisher=] ] |access-date=June 13, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160305013711/https://www.doi.gov/oia/islands/disputedislands |archive-date=March 5, 2016 }}</ref><ref>{{cite web
|url=https://treaties.un.org/doc/Publication/UNTS/Volume%201643/v1643.pdf
|title=Treaty of Friendship between the United States of America and the Republic of Kiribati
|pages=239–250
|access-date=June 17, 2015
|url-status=live
|archive-url=https://web.archive.org/web/20160304230003/https://treaties.un.org/doc/Publication/UNTS/Volume%201643/v1643.pdf
|archive-date=March 4, 2016
}}</ref>


The United States recognized the sovereignty of ] over ], ], ], and ].<ref name="doi-former"/><ref>{{cite web
==1820s==
|url=https://treaties.un.org/doc/Publication/UNTS/Volume%202011/v2011.pdf
]
|title=Treaty of Friendship between the United States of America and Tuvalu
;] ]
|pages=79–84
The ] of ] was split off and admitted as the 23rd state, ].
|access-date=June 17, 2015
{{-}}
|url-status=live
|archive-url=https://web.archive.org/web/20160304200403/https://treaties.un.org/doc/Publication/UNTS/Volume%202011/v2011.pdf
|archive-date=March 4, 2016
}}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|October 12, 1984
|The ] made its judgment on where the maritime border should be in the ] between the United States and Canada.<ref>
{{Webarchive|url=https://web.archive.org/web/20160817084511/http://www.icj-cij.org/docket/index.php?p1=3&p2=3&k=6f&case=67&code=cigm&p3=4 |date=August 17, 2016 }} , accessed June 30, 2015
</ref><ref name="maritime"/> No land changed hands. The scope of the case did not include the sovereignty of Machias Seal Island, but the judgment enabled defining the extent of the disputed water area around that island (an area of 210 square nautical miles).<ref name="IBRU"/>
|align="center"|''no change to map''
|-
!scope=row|October 21, 1986
|The Marshall Islands District of the ] became independent as the ].<ref name="proclamation-5564"/> The Marshall Islanders had claimed ] as part of their territory since at least 1973, and continued that after independence.<ref>{{cite news|last=Anderson |first=Jon |date=February 8, 1973 |title=Wake Island Claimed By Marshall Islanders |url=https://www.newspapers.com/clip/3864881/wake_island_claimed_by_marshall_islands/ |access-date=January 28, 2016 |newspaper=The Cameron Herald |location=Cameron, Texas |url-status=live |archive-url=https://web.archive.org/web/20160819040955/https://www.newspapers.com/clip/3864881/wake_island_claimed_by_marshall_islands/ |archive-date=August 19, 2016 }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|November 3, 1986
|Most of the ] was dissolved by the ]. The districts of Chuuk, Pohnpei, and Yap became independent as the ]. The Mariana Islands District, having already been taking moves towards integration with the United States, became a territory of the United States, the ].<ref name="proclamation-5564">{{cite web|url=http://www.gpo.gov/fdsys/pkg/STATUTE-101/pdf/STATUTE-101-Pg2027.pdf |title=Proclamation 5564: Placing Into Full Force and Effect the Covenant With the Commonwealth of the Northern Mariana Islands, and the Compacts of Free Association With the Federated States of Micronesia and the Republic of the Marshall Islands |author=Ronald Reagan |date=November 3, 1986 |access-date=April 7, 2015 |publisher=] |url-status=live |archive-url=https://web.archive.org/web/20160924011909/https://www.gpo.gov/fdsys/pkg/STATUTE-101/pdf/STATUTE-101-Pg2027.pdf |archive-date=September 24, 2016 |author-link=Ronald Reagan }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|June 1, 1990
|The maritime border between the United States and the ] was provisionally defined.<ref>{{cite web|url=https://www.un.org/depts/los/LEGISLATIONANDTREATIES/PDFFILES/TREATIES/USA-RUS1990MB.PDF|title=Agreement between the United States of America and the Union of Soviet Socialist Republics on the maritime boundary|date=1 June 1990|publisher=The United Nations}}</ref><ref name="maritime"/> The two countries agreed on this date to abide by the terms of the treaty pending its ratification and entry into force,<ref> {{webarchive|url=https://web.archive.org/web/20160821224834/https://treaties.un.org/doc/Publication/UNTS/Volume%202262/v2262.pdf |date=August 21, 2016 }}, signed June 1, 1990; ] 40300; accessed July 1, 2015</ref> but while it was ratified by the United States Senate on September 16, 1991,<ref>{{USTreaty|101|22}}</ref> it was never ratified by the Soviet Union or its successor state, ].
|align="center"|''no change to map''
|-
!scope=row|October 1, 1994
|The remaining district of the ], the Palau District, became independent as the ], dissolving the TTPI.<ref>{{cite news |title=Palau Gains Independence on Saturday |agency=Associated Press |location=Salt Lake City, Utah, USA |date=September 30, 1994 |url=https://news.google.com/newspapers?id=LOZHAAAAIBAJ&pg=5945,7792568&dq=palau&hl=en }}</ref>
|align="center"|Pacific Ocean:<br />]
|-
!scope=row|June 1, 1995
|The maritime border between the United States and territories of the ] in the ] was defined.<ref name="maritime"/><ref> {{webarchive|url=https://web.archive.org/web/20160331131528/https://treaties.un.org/doc/Publication/UNTS/Volume%201913/v1913.pdf |date=March 31, 2016}}, signed May 11, 1993; ] 32636; accessed July 1, 2015</ref><ref> {{webarchive|url=https://web.archive.org/web/20160331131528/https://treaties.un.org/doc/Publication/UNTS/Volume%201913/v1913.pdf |date=March 31, 2016}}, signed May 11, 1993; ] 32637; accessed July 1, 2015</ref>
|align="center" rowspan=3|''no change to map''
|-
!scope=row|January 16, 1997
|] was transferred to the ].<ref name="doi-navassa">{{cite web|url=https://www.doi.gov/oia/islands/navassa |title=Navassa Island |date=12 June 2015 |publisher=] ] |access-date=July 15, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160815201647/https://www.doi.gov/oia/islands/navassa |archive-date=August 15, 2016 }}</ref><ref>{{Dead link|date=January 2023 |bot=InternetArchiveBot |fix-attempted=yes }}, ] ], signed January 16, 1997, accessed June 30, 2015</ref>
|-
!scope=row|November 13, 1997
|The maritime border between the United States and ] was defined.<ref name="maritime"/><ref> {{webarchive|url=https://web.archive.org/web/20160304140922/https://treaties.un.org/doc/Publication/UNTS/Volume%202143/v2143.pdf |date=March 4, 2016}}, signed May 4, 1978; ] 37399; accessed June 30, 2015</ref>
|-
!scope=row|May 26, 1998
|The ] ] that extra land added to ] since the original island was officially granted to ] in an interstate compact with ] in 1834 belonged to New Jersey, because the island was within the territorial waters of New Jersey. The original natural boundary of Ellis Island remained an enclave of New York.<ref>{{cite web|url=http://supreme.justia.com/cases/federal/us/523/767/|title=New Jersey v. New York – 523 U.S. 767 (1998)|publisher=Justia|access-date=August 2, 2012}}</ref>
|align="center"|]
|-
!scope=row|December 31, 1999
|All former ] parcels not turned over since 1979, as well as all joint canal operations areas, were transferred to ].
|align="center"|''too small to map''
|-
!scope=row|January 17, 2001
|The maritime border between the United States and ] on the continental shelf in the western Gulf of Mexico beyond 200 nautical miles was defined.<ref name="maritime"/><ref> {{webarchive|url=https://web.archive.org/web/20160304140922/https://treaties.un.org/doc/Publication/UNTS/Volume%202143/v2143.pdf |date=March 4, 2016}}, signed June 9, 2000; ] 37400; accessed June 30, 2015</ref>
|align="center"|''no change to map''
|-
!scope=row|November 24, 2009
|Six islands along the ] were ceded from ] to ], and three islands and two bancos were ceded from Mexico to Texas. The transfer, which had been pending for 20 years, was the first application of Article III of the ].<ref name="maritime"/><ref name="bancos"/><ref name="minute315">{{cite web |url=http://www.ibwc.state.gov/Files/Minutes/Joint_Report_315.pdf |title=Minute 315: Adoption of the Delineation of the International Boundary on the 2008 Aerial Photographic Mosaic of the Rio Grande |publisher=] |date=November 24, 2009 |access-date=June 13, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160411202233/http://www.ibwc.state.gov/Files/Minutes/Joint_Report_315.pdf |archive-date=April 11, 2016 }}</ref>
|align="center"|''too small to map''
|-
!scope=row|September 23, 2014
|The maritime border between the United States and ] was ].<ref name="maritime"/><ref>{{USTreaty|105|53}}</ref> The treaty was signed on May 13, 1997, but it was not ratified by the United States until at least 2002, and the ] shows it as entering into force on this date.<ref>{{cite web|url=https://treaties.un.org/pages/showDetails.aspx?objid=08000002804248ee |title=Treaty between the Government of Niue and the Government of the United States of America on the delimitation of a maritime boundary |publisher=] |access-date=June 30, 2015 |url-status=live |archive-url=https://web.archive.org/web/20160821191110/https://treaties.un.org/pages/showDetails.aspx?objid=08000002804248ee |archive-date=August 21, 2016 }}</ref>
|align="center"|''no change to map''
|-
!scope=row|January 1, 2017
|The border between ] and ] was clarified following years of surveys and negotiation, moving 19 homes across state lines.<ref>{{cite news|url=http://abc7ny.com/news/border-of-north-and-south-carolina-shifted-on-january-1st/1678605/ |title=Border of North Carolina and South Carolina Realigned on January 1st |work=WABC |date=January 2, 2017 |access-date=January 3, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170103131022/http://abc7ny.com/news/border-of-north-and-south-carolina-shifted-on-january-1st/1678605/ |archive-date=January 3, 2017 }}</ref><ref>{{cite news|url=https://www.nytimes.com/2014/08/24/opinion/sunday/how-the-carolinas-fixed-their-blurred-lines.html |title=How the Carolinas Fixed Their Blurred Lines |work=The New York Times |date=August 23, 2014 |access-date=January 3, 2017 |url-status=live |archive-url=https://web.archive.org/web/20160524000946/http://www.nytimes.com/2014/08/24/opinion/sunday/how-the-carolinas-fixed-their-blurred-lines.html |archive-date=May 24, 2016 }}</ref>
|align="center"|''too small to map''
|-
!scope=row|November 30, 2020
|The ] adopted a constitutional amendment, renaming itself the State of Rhode Island.<ref></ref><ref></ref>
|align="center"|]
|}


==Bancos along the Rio Grande==
]
]
;] ]
The ] between the United States and ] allowed, in the event of sudden changes in the course of the ] (as by flooding), for the border to be altered to follow the new course.<ref>{{cite web|url=http://www.ibwc.state.gov/Files/Convention_of_1905.pdf |title=Convention Between the United States and Mexico for the Elimination of the Bancos in the Rio Grande from the Effects of Article II of the Treaty of November 12, 1884 |date=June 5, 1907 |access-date=April 19, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20151009042029/http://www.ibwc.state.gov/Files/Convention_of_1905.pdf |archive-date=October 9, 2015 }}</ref> The sudden changes often created ''bancos'' (land surrounded by bends in the river that became segregated from either country by a cutoff, often due to rapid accretion or avulsion of the alluvial channel), especially in the Lower Rio Grande Valley. When these bancos are created, the ] investigates if land previously belonging to the United States or ] is to be considered on the other side of the border.<ref>{{cite web |last=Metz |first=Leon C. |date=June 12, 2010 |title=Bancos of the Rio Grande |url=https://www.tshaonline.org/handbook/online/articles/rnb08 |work=Handbook of Texas Online |publisher=Texas State Historical Association |access-date=July 13, 2015 |archive-url=https://web.archive.org/web/20161027194705/https://www.tshaonline.org/handbook/online/articles/rnb08%29 |archive-date=October 27, 2016 |url-status=live}}</ref> In all cases of these adjustments along the Rio Grande under the 1905 convention, which occurred on 37 different dates from 1910 to 1976, the transferred land was minuscule (ranging from one to 646 acres) and uninhabited.<ref>{{cite web | url=https://www.ibwc.gov/Treaties_Minutes/Minutes.html | title=IBWC Minutes | publisher=] | access-date=September 11, 2017}}</ref><ref>{{cite web | url=http://www.google.com/maps/d/edit?mid=zTEHCtUumBXk.k-ueCthwuSNs | title=USA-Mexico Bancos Map | access-date=September 11, 2017}}</ref><ref>{{cite book |title=Restless River, International Law and the Behavior of the Rio Grande |publisher=Texas Western Press |author=Mueller, Jerry E. |year=1975 |page=64 |isbn=9780874040500}}</ref>
The ] came in to effect. It established the entirety of the border between the United States and ]. Under the terms of the treaty, both Floridas were also sold to the United States.
{{-}}


==See also==
]
{{commons category|Maps of the territorial evolution of the United States}}
;] ]
* ]
The southeastern portion of ] was admitted as the 24th state, ]. The remainder became unorganized.
* ]
{{-}}
* ]
* ]
* ]
* ]
* ]
* ]
* ] (annexation of Cuba)
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* ]


==Notes==
]
{{notelist}}
;] ]
] and the portion of ] not already part of other states were combined and organized as ]. Around this time, the official spelling of Arkansaw Territory (which had no official spelling before) became Arkansas Territory.<ref name="statoids" /> Also, on ] ], the Viceroyality of New Spain achieved independence as ].
{{-}}


==References==
]
{{reflist}}
;] ]
] was shrunk, the western portion becoming unorganized.
{{-}}


==Further reading==
]
* {{cite book | last=Rohrbough |first=M. J. | date=1978 | title=The Trans-Appalachian Frontier: People, Societies, and Institutions, 1775-1850 | title-link=The Trans-Appalachian Frontier: People, Societies, and Institutions, 1775-1850 | author-link=Malcolm J. Rohrbough | publisher=Oxford University Press | isbn=978-0-19-502209-4}}
;] ]
* {{cite book |last=Stein |first=Mark |author-link=Mark Stein (author) |year=2008 |title=How the States Got Their Shapes |url=https://books.google.com/books?id=w6UQZLmZ6LEC |location=New York |publisher=Smithsonian Books/Collins |isbn=978-0-06-143138-8 |oclc=137324984}}
] was shrunk further, the remainder again becoming unorganized.
* {{cite book |author=Van Zandt, Franklin K. |year=1976 |url=https://archive.org/details/bub_gb_skxAAAAAIAAJ |title=Boundaries of the United States and the Several States: With Miscellaneous Geographic Information Concerning Areas, Altitudes, and Geographic Centers |location=Washington, D.C. |publisher=] |oclc=69426475}}
{{-}}
* {{cite book | title=Statistical Atlas of the United States | pages=65–79 | author=Walker, Francis A. | year=1874 | publisher= J. Bien, lith. | url=https://archive.org/details/statisticalatla00unit/page/n5 | access-date=April 3, 2019}}


{{Territorial evolution of the world}}
==1830s==
] {{United States topics}}
{{US history}}
;] ]
{{American frontier}}
A large portion of unorganized land was added to ].
{{Thirteen Colonies}}
{{-}}
{{Territories of the United States}}

{{Former sovereign or unrecognized states within the United States}}
]
{{featured list}}
;] ]
The ] achieved independence from ], though with a large portion of the territory disputed.
{{-}}

]
;] ]
] was admitted as the 25th state, ].
{{-}}

]
;] ]
] was split off from ], leaving the latter only with the lower peninsula and a small portion of the upper peninsula.<ref name="NWT" />
{{-}}

]
;] ]
As a consolation for giving up the ], the whole of the present-day ] was transferred from ] to ].<ref name="NWT" />
{{-}}

]
;] ]
] was admitted as the 26th state, ].
{{-}}

]
;] ]
The ] added a small area of land to ], giving it its present-day boundaries.
{{-}}

]
;] ]
] was split off from ].
{{-}}

==1840s==
]
;] ]
The ] settled the border between the United States and lands held by the United Kingdom east of the ].
{{-}}

]
;] ]
] was admitted as the 27th state, ].
{{-}}

]
;] ]
The ] was annexed by the United States and admitted as the 28th state, ]. It brought with it all the lands of ] that it claimed.
{{-}}

]
;] ]
The ] established the ] west of the Lake of the Woods as the continental border (so it did not include ]) with the lands held by the United Kingdom. The sharing of ] ended, and the American portion becomes unorganized territory.
{{-}}

]
;] ]
The southeast portion of ] was admitted as the 29th state, ]. The remainder became unorganized.
{{-}}

]
;] ]
The ], ending the ], granted a ] to the United States from ].
{{-}}

]
;] ]
The southeastern portion of ] was admitted as the 30th state, ]. The remainder became unorganized.
{{-}}

]
;] ]
] was organized.
{{-}}

]
;] ]
] was organized.
{{-}}

==1850s==
]
;] ]
The ] was divided. The western portion was admitted as the 31st state, ]. The rest was organized as ] and ]. Both territories also included land ceded to the federal government by ] in exchange for taking on its debts; a portion of Texas and the Mexican Cession became unorganized land. A pecularity appeared at this time, when a small strip of land north of Texas was not officially assigned by any state or territory; this came to be called the ] or "No Man's Land".
{{-}}

]
;] ]
] was split from ].
{{-}}

]
;] ]
The ] added some land to ]. At this time, the external borders of the ] became what they are today.
{{-}}

]
;] ]
] and ] were organized; the remaining unorganized land colloquially became known as ].
{{-}}

]
;] ]
The eastern portion of ] was admitted as the 32nd state, ]. The remainder became unorganized.
{{-}}

]
;] ]
The western portion of ] was admitted as the 33rd state, ]. The remainder was assigned to ].
{{-}}

==1860s==
]
;] ]
Texas began claiming ], controlled at that time by the federal government as unorganized territory.
{{-}}

]
;] ]
The eastern portion of ] was admitted as the 34th state, ]. A pecularity arose for the western portion. It was added to ] on ] ]; however, for the month between statehood for Kansas and the Colorado Territory being formed, it appears to have had no official status. It was '']'' under the control of the self-proclaimed ].
{{-}}

]
;] ]
The ] (CSA) was formed. The ] ] at different dates and joined the CSA at different dates; to simplify the map, only the final form of the CSA is shown here. There were ] as well as ] governments in ] and ], and the CSA had full control over ].
{{-}}

]
;] ]
] was organized, with land from ], ], and ] Territories, as well as the land left over from ].
{{-}}

]
;] ]
] was split from ], and included the unorganized land left over from ]. ] was split from ].
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]
;] ]
The ] established ] in the southern half of the Union's ]. It would be organized on ] ].
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]
;] ]
A strip of land on the western side of ] was transferred to ].
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]
;] ]
The Union created its own ], splitting it off from ].
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]
;] ]
] was created from portions of ], ], and ] Territories.
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]
;] ]
Several counties of northwestern ] who didn't want to be part of the ] split off and were admitted as the 35th state, ].
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]
;] ]
] was split from ], which also had some land transferred to ].
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]
;] ]
] was admitted as the 36th state, ].
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]
;] ]
The ] ]. The process of ] and readmission to the union would take several years; to simplify the map, they are shown as already readmitted.
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]
;] ]
A strip of ]'s western land was transferred to the state of ].
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]
;] ]
The northwestern corner of ] was transferred to the state of ], giving it its present-day borders.
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]
;] ]
] was admitted as the 37th state, ].
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]
;] ]
The United States ] from ]; it was designated the ].
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==1870s==
]
;] ]
] was formed from portions of ], ], and ] Territories.
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]
;] ]
] was admitted as the 38th state, ].
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==1880s==
]
;] ]
The ] was redesignated the ].
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]
;] ]
] was split in two, and it was admitted as the 39th state, ], and 40th state, ].
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]
;] ]
] was admitted as the 41st state, ].
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]
;] ]
] was admitted as the 42nd state, ].
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==1890s==
]
;] ]
] was organized from the western portion of ], and it included the ].
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]
;] ]
] was admitted as the 43rd state, ].
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]
;] ]
] was admitted as the 44th state, ].
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]
;] ]
] was admitted as the 45th state, ]. Also of note, on ] ], the ] became the ].
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]
;] ]
A ] ruling officially assigns ] to ].
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]
;] ]
The ] was annexed by the United States. It was organized in to the ] on ] ].
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==20th century==
]
;] ]
] and ] were combined and admitted as the 46th state, ].
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]
;] ]
] was admitted as the 47th state, ].
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]
;] ]
] was admitted as the 48th state, ].
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]
;] ]
The ] was organized as ].
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]
;] ]
] was admitted as the 49th state, ].
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]
;] ]
] was admitted as the 50th state, ], resulting in the present-day situation of the United States.
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==References==
<div class="references-small">
<references/>
</div>

==See also==
*]
*]
*]
*]


] ]
]
]
]
]
]
]

Latest revision as of 13:51, 25 December 2024

"Westward expansion" redirects here. For trails in the American Old West, see Westward Expansion Trails.
Animated map of the territorial evolution of the United States
US Census Bureau map depicting territorial acquisitions, 2007
After Japan's defeat in World War II, the Japanese-ruled Northern Mariana Islands came under control of the United States.

The United States of America was formed after thirteen British colonies in North America declared independence from the British Empire on July 4, 1776. In the Lee Resolution, passed by the Second Continental Congress two days prior, the colonies resolved that they were free and independent states. The union was formalized in the Articles of Confederation, which came into force on March 1, 1781, after being ratified by all 13 states. Their independence was recognized by Great Britain in the Treaty of Paris of 1783, which concluded the American Revolutionary War. This effectively doubled the size of the colonies, now able to stretch west past the Proclamation Line to the Mississippi River. This land was organized into territories and then states, though there remained some conflict with the sea-to-sea grants claimed by some of the original colonies. In time, these grants were ceded to the federal government.

The first great expansion of the country came with the Louisiana Purchase of 1803, which doubled the country's territory, although the southeastern border with Spanish Florida was the subject of much dispute until it and Spanish claims to the Oregon Country were ceded to the US in 1821. The Oregon Country gave the United States access to the Pacific Ocean, though it was shared for a time with the United Kingdom. The annexation of the Republic of Texas in 1845 led directly to the Mexican–American War, after which the victorious United States obtained the northern half of Mexico's territory, including what was quickly made the state of California.

As the development of the country moved west, however, the question of slavery became more important, with vigorous debate over whether the new territories would allow slavery and events such as the Missouri Compromise and Bleeding Kansas. This came to a head in 1860 and 1861, when the governments of the southern states proclaimed their secession from the country and formed the Confederate States of America. The American Civil War led to the defeat of the Confederacy in 1865 and the eventual readmission of the states to the United States Congress. The cultural endeavor and pursuit of manifest destiny provided a strong impetus for westward expansion in the 19th century.

The United States began expanding beyond North America in 1856 with the passage of the Guano Islands Act, causing many small and uninhabited, but economically important, islands in the Caribbean Sea and the Pacific Ocean to be claimed. Most of these claims were eventually abandoned, largely because of competing claims from other countries. The Pacific expansion culminated in the annexation of Hawaii in 1898, after the overthrow of its government five years previously. Alaska, the last major acquisition in North America, was purchased from Russia in 1867. Support for the independence of Cuba from the Spanish Empire, and the sinking of the USS Maine, led to the Spanish–American War in 1898, in which the United States gained Puerto Rico, Guam, and the Philippines, and occupied Cuba for several years. American Samoa was acquired by the United States in 1900 after the end of the Second Samoan Civil War. The United States purchased the U.S. Virgin Islands from Denmark in 1917. Puerto Rico and Guam remain territories, and the Philippines became independent in 1946, after being a major theater of World War II.

Following the war, many islands were entrusted to the U.S. by the United Nations, and while the Northern Mariana Islands became a U.S. territory, the Marshall Islands, Federated States of Micronesia, and Palau emerged from the trust territory as independent nations. The last major international change was the acquisition in 1904, and return to Panama in 1979, of the Panama Canal Zone, an unincorporated US territory which controlled the Panama Canal. The final cession of formal control over the region was made to Panama in 1999.

States have generally retained their initial borders once established. Only three states (Kentucky, Maine, and West Virginia) have been created directly from area belonging to another state (although at the time of admission, Vermont agreed to a monetary payment for New York to relinquish its claim); all of the other states were created from federal territories or from acquisitions. Four states (Louisiana, Missouri, Nevada, and Pennsylvania) have expanded substantially by acquiring additional federal territory after their initial admission to the Union. In 1912, Arizona was the last state established in the contiguous United States, commonly called the "lower 48". In 1959, Hawaii was the 50th and most recent state admitted.

Legend for maps

Key to map colors
  United States states (domestic maps), undisputed area of United States (dispute maps)
  United States territories (domestic maps)
  disputed area of United States
  area changed by event

1776–1784 (American Revolution)

Date Event Change Map
July 4, 1776 Thirteen colonies of the Kingdom of Great Britain in North America collectively declared their independence as the United States of America, though several colonies had already individually declared independence:

The capital was not specifically established; at the time, the Continental Congress met in Philadelphia.

Many states had vaguely defined and surveyed borders; these are not noted as contested in the maps unless there was an active dispute. The borders of North Carolina were particularly poorly surveyed, its border with South Carolina having been done in several pieces, none of which truly matched the spirit of the charter, and its border with Virginia was only surveyed roughly halfway inland from the sea.

Several northeastern states had overlapping claims: Connecticut, Massachusetts Bay, and New York all claimed land west of their accepted borders, overlapping with each other and with a sizable claim by Virginia. Of the three, only Connecticut seriously pursued its claims, while Virginia is considered to have had the most legitimate claim to the vast northwest, dividing it into counties and maintaining some limited control.

The entirety of the new United States was claimed by Great Britain, including Machias Seal Island and North Rock, two small islands off the northeast coast which remain disputed up to the present.

Map of the change to the United States in central North America on July 4, 1776

Disputes:

Map of the international disputes involving the United States in central North America from July 4, 1776, to January 15, 1777

September 20, 1776 The Counties of New Castle, Kent, and Sussex, upon Delaware enacted a constitution, renaming itself the Delaware State. Map of the change to the United States in central North America on September 20, 1776
September 28, 1776 The State of Pennsylvania enacted a constitution, renaming itself the Commonwealth of Pennsylvania. no change to map
December 20, 1776 To avoid British forces who were advancing on Philadelphia, the Continental Congress began meeting in Baltimore. Map of the change to the United States in central North America on December 20, 1776
January 15, 1777 The northeastern region of New York, known as the New Hampshire Grants, declared independence as New Connecticut. Disputes:

Map of the change to the international disputes involving the United States in central North America on January 15, 1777

March 4, 1777 The Continental Congress returned to Philadelphia after the threat to it by British forces ended. Map of the change to the United States in central North America on March 4, 1777
June 4, 1777 New Connecticut was renamed Vermont. Disputes:

Map of the change to the international disputes involving the United States in central North America on June 4, 1777

September 27, 1777 The Continental Congress fled Philadelphia after the American defeat at the Battle of Brandywine, and briefly met in Lancaster, Pennsylvania Map of the change to the United States in central North America on September 27, 1777
September 30, 1777 The Continental Congress continued to move away from Philadelphia, settling in York, Pennsylvania. Map of the change to the United States in central North America on September 30, 1777
June 11, 1778 Vermont claimed what was called the "East Union", consisting of some towns in New Hampshire that petitioned on March 12, 1778, to join with Vermont, out of concern that their state was focusing too much on its coastal region. Vermont never gained full control over the area. Disputes:
Map of the change to the international disputes involving the United States in central North America on June 11, 1778
October 21, 1778 Under pressure from the Continental Congress, Vermont rescinded the annexation of the East Union; the legislature declared on February 12, 1779, that the East Union should be considered null from its beginning. Disputes:
Map of the change to the international disputes involving the United States in central North America on October 21, 1778
July 2, 1779 The Continental Congress returned to Philadelphia following British withdrawal. Map of the change to the United States in central North America on July 2, 1779
August 31, 1779 Virginia surrendered its claim to southwest Pennsylvania. Map of the change to the United States in central North America on August 31, 1779
March 23, 1780 North Carolina and Virginia surveyed their border further inland. Virginia's survey reached the Tennessee River on this date, while North Carolina's team stopped at the Cumberland Gap and filed their survey on November 17, 1779. The two surveys were roughly two miles apart, creating a thin area claimed by both states. While the border was intended to follow 36°30′ north, early surveying errors caused it to veer north of that, reaching a distance of almost ten miles off by the time it reached the Tennessee River. Map of the change to the United States in central North America in March 1780
October 25, 1780 The State of Massachusetts Bay enacted a constitution, renaming itself the Commonwealth of Massachusetts. Map of the change to the United States in central North America on October 25, 1780
March 1, 1781 The Articles of Confederation entered into force. no change to map
April 4, 1781 Vermont again claimed an East Union, consisting of some towns in New Hampshire that wished to join with Vermont; more towns were interested than during the first attempt in 1778, though again, the exact extent of the borders is unknown. Vermont never gained full control over the area. Disputes:
Map of the change to the international disputes involving the United States in central North America on April 4, 1781
June 16, 1781 Vermont claimed what was called the "West Union", consisting of some towns in New York, mainly to counterbalance Vermont's attempt at eastward expansion. Vermont never gained full control over the area. The specific date this occurred is unclear; sources suggest June 16, June 26, and July 18. Disputes:
Map of the change to the international disputes involving the United States in central North America on June 16, 1781
February 22, 1782 Vermont abandoned its attempts to annex the East Union from New Hampshire and the West Union from New York. Disputes:
Map of the change to the international disputes involving the United States in central North America on February 22, 1782
October 29, 1782 The federal government accepted the cession from New York of its western claims, which the state ceded on February 19, 1780, and executed on March 1, 1781; New York proclaimed its new western border to be a line drawn south from the western end of Lake Ontario. At its maximum interpretation, the state had claimed an area bounded by Lake Erie, Lake Huron and Lake Michigan; to the Illinois, Mississippi, and Tennessee Rivers; and north along the Appalachian Mountains, ending at the border with Pennsylvania. It is unclear from where this claim came; many sources state that New York had surrendered it, but very few elaborate on how it was obtained. One source states that it was a cession by the Six Nations, who had conquered much of the region. However, New York never seriously enforced these claims. The cession included the small tip of New York north of Pennsylvania, which came to be known as the Erie Triangle. Map of the change to the United States in central North America on October 29, 1782
December 30, 1782 The Congress of the Confederation declared that the land that Connecticut claimed in northern Pennsylvania was part of Pennsylvania, thus attempting to end the Pennamite–Yankee War. The claim was an extension of Connecticut's northernmost and southernmost borders westward, skipping New Jersey and New York, though as Connecticut's northern border was a few miles north of Pennsylvania's northern border, a small sliver of New York was also claimed. While conflict would continue for some time, this was the end of the formal claim by Connecticut. Map of the change to the United States in central North America on December 30, 1782
June 30, 1783 The Pennsylvania Mutiny of 1783, and the Pennsylvania government reaction to it, caused the Congress of the Confederation to leave Philadelphia for Princeton. Map of the change to the United States in central North America on June 30, 1783
November 26, 1783 The Congress of the Confederation reconvened in Annapolis. Map of the change to the United States in central North America on November 26, 1783
March 1, 1784 Virginia ceded its claims northwest of the Ohio River to the federal government. Connecticut continued to claim its western lands that had overlapped with Virginia's cession. Map of the change to the United States in central North America on March 1, 1784
May 12, 1784 Great Britain recognized the independence of the United States, ending its claim to the country. The treaty ended the American Revolutionary War, though military action had largely ended after the Franco-American victory at Yorktown on October 19, 1781.

Because of ambiguities and poor knowledge of geography, the treaty was unclear in several areas:

The Peace of Paris also involved treaties with France and Spain, with Great Britain ceding the Floridas to Spain. During their ownership of West Florida, the British had moved its border north, and the cession to Spain appeared to apply to the full extent of the British colony. However, the British-American treaty granted the extension of West Florida to the United States, where it enlarged Georgia south to 31° north, indicating that only the original definition of West Florida was to be ceded to Spain. The local Spanish governors also made a move to occupy forts along the Mississippi River, with claims to everything south of the Tennessee River; it is unknown how official or strong these claims were, and they are not mapped as they are in conflict with the other Spanish claim involving the border of West Florida.

Map of the change to the United States in central North America on May 12, 1784

Disputes:
Map of the change to the international disputes involving the United States in central North America on May 12, 1784

1784–1803 (Organization of territory)

Date Event Change Map
August 23, 1784 A region in central North Carolina (modern-day eastern Tennessee), unhappy with the state's governance over the area, declared independence from the state as the State of Franklin. The government of Franklin held some control over the area, and petitioned for statehood, receiving support from seven of the nine states required, but would only last a few years. Unofficial change:
Map of the change to the United States in central North America on August 23, 1784
November 1, 1784 The Congress of the Confederation moved for a short time to Trenton. Map of the change to the United States in central North America on November 1, 1784
January 11, 1785 The Congress of the Confederation moved to New York, and would settle there for five years. Map of the change to the United States in central North America on January 11, 1785
April 19, 1785 The federal government accepted the cession from Massachusetts of its extreme western claim, which was never seriously enforced. Change on paper only:
Map of the change to the United States in central North America on April 19, 1785
September 13, 1786 Connecticut surrendered its western claim to the federal government except for its Western Reserve, though it is unclear how much control they held over the ceded region. Change on paper only:
Map of the change to the United States in central North America on September 13, 1786
December 16, 1786 Massachusetts surrendered its claim to western New York, though it is unclear if Massachusetts ever held control over the region, as the claim was to the "soil, not the sovereignty". This land was later known as the Phelps and Gorham Purchase. Change on paper only:
Map of the change to the United States in central North America on December 16, 1786
July 13, 1787 The Territory Northwest of the River Ohio, ceded earlier by Virginia, was organized and commonly became known as the Northwest Territory. Map of the change to the United States in central North America on July 13, 1787
August 9, 1787 South Carolina ceded its western claim to the federal government, though it was a result of inaccurate geography and South Carolina never actually held claim to this land. The claim was of a strip of land between the border of North Carolina and the source of the Tugaloo River but, unknown at the time, the river originated in North Carolina. The eastern part of this cession would be given to Georgia in 1802, despite Georgia technically already having claim to the land. Change on paper only:
Map of the change to the United States in central North America on August 9, 1787
December 7, 1787 Delaware became the first state to ratify the United States Constitution. no change to map
December 12, 1787 Pennsylvania became the second state to ratify the Constitution.
December 18, 1787 New Jersey became the third state to ratify the Constitution.
January 2, 1788 Georgia became the fourth state to ratify the Constitution.
January 9, 1788 Connecticut became the fifth state to ratify the Constitution.
February 6, 1788 Massachusetts became the sixth state to ratify the Constitution.
April 28, 1788 Maryland became the seventh state to ratify the Constitution.
May 23, 1788 South Carolina became the eighth state to ratify the Constitution.
June 21, 1788 New Hampshire became the ninth state to ratify the Constitution; at this point, the Constitution became the active governing document of those nine states having ratified the same (per Article VII).
June 25, 1788 Virginia became the tenth state to ratify the Constitution.
July 26, 1788 New York became the eleventh state to ratify the Constitution.
February 1789 John Sevier, governor of the State of Franklin, pledged allegiance to North Carolina at the February term of the Greene County Court, effectively ending the claimed independence of Franklin. Unofficial change:
Map of the change to the United States in central North America in February 1789
August 7, 1789 The Northwest Territory was reorganized under the Constitution. no change to map
November 21, 1789 North Carolina became the twelfth state to ratify the Constitution.
April 2, 1790 North Carolina ceded its western half to the federal government. Map of the change to the United States in central North America on April 2, 1790
May 26, 1790 The land recently ceded by North Carolina was organized as the Territory South of the River Ohio, commonly known as the Southwest Territory. Map of the change to the United States in central North America on May 26, 1790
May 29, 1790 Rhode Island became the thirteenth state to ratify the Constitution. no change to map
December 6, 1790 Per the Residence Act, the Congress of the United States relocated to Philadelphia for ten years until a federal district was built and ready. Map of the change to the United States in central North America on December 6, 1790
March 4, 1791 Vermont, which had been considered part of New York despite acting independently since 1777, was admitted as the fourteenth state. Map of the change to the United States in central North America on March 4, 1791

Disputes:
Map of the change to the international disputes involving the United States in central North America on March 4, 1791
March 30, 1791 The District of Columbia, a federal district planned to house the federal government by 1800, was formed from land ceded by Maryland and Virginia, consisting of a 100 square mile diamond, with its southern tip at Jones Point, straddling the Potomac River. However, it was not yet given that name, being simply referred to as the federal district. In September 1791, the commissioners in charge of planning the city would term it the "Territory of Columbia", and various laws refer to a District of Columbia, but sometimes informally. The area does not appear to have been formally named "District of Columbia" until at least the organic act of 1871. Since the name "Columbia" was used from very early on, and at least informally by the government, the map will use "District of Columbia" starting from this date. Map of the change to the United States in central North America on March 30, 1791
March 3, 1792 Pennsylvania purchased the Erie Triangle from the federal government. Map of the change to the United States in central North America on March 3, 1792
June 1, 1792 The western half of Virginia, which the state had agreed in 1789 to cede to the federal government, was admitted as the fifteenth state, Kentucky. Map of the change to the United States in central North America on June 1, 1792
June 12, 1792 The Delaware State enacted a new constitution, renaming itself the State of Delaware. no change to map
August 3, 1795 Representatives of the United States and the Western Confederacy sign the Treaty of Greenville, ending the Northwest Indian War and ceding most of the modern state of Ohio to United States control.
February 29, 1796 Great Britain agreed to abandon several forts in the northwest that it still occupied, including Detroit. The Jay Treaty also provided for commissions to determine the border between the northwestern point of the Lake of the Woods and the source of the Mississippi River, and which river to consider the St. Croix River.
April 25, 1796 The northern half of West Florida was ceded by Spain, resolving the dispute over the region. Disputes:
Map of the change to the international disputes involving the United States in central North America on April 25, 1796
June 1, 1796 The Southwest Territory was admitted as the sixteenth state, Tennessee. Map of the change to the United States in central North America on June 1, 1796
April 7, 1798 In response to the Yazoo Land Fraud, an act authorized President John Adams to appoint commissioners to negotiate with Georgia about ceding its western land. The act created Mississippi Territory from the southwestern quarter of Georgia in the region recently ceded by West Florida, while maintaining that Georgia still held rights over the territory. Map of the change to the United States in central North America on April 7, 1798
October 25, 1798 Commissioners agreed on the source of the St. Croix River, setting the lower portion of the border between Massachusetts and Great Britain and, thus, where the eastern north–south line originated. Map of the change to the United States in central North America on October 25, 1798

Disputes:
Map of the change to the international disputes involving the United States in central North America on October 25, 1798
June 9, 1800 Connecticut ceded its Western Reserve to the federal government, which assigned it to the Northwest Territory. The act doing so was passed in Congress on April 28, 1800, and Connecticut approved it on this date. Map of the change to the United States in central North America on June 9, 1800
July 4, 1800 Indiana Territory was organized from the western half of Northwest Territory. Map of the change to the United States in central North America on July 4, 1800
November 17, 1800 The Congress of the United States moved to Washington in the District of Columbia, now built and ready to be the capital. This was two weeks before the December 1 date established in the Residence Act; President John Adams urged Congress to move early in hopes of securing enough Southern votes to be re-elected, though this failed. Map of the change to the United States in central North America on November 17, 1800
January 1, 1801 The Kingdom of Great Britain united with the Kingdom of Ireland, renaming itself the United Kingdom. Disputes:
Map of the change to international disputes involving the United States in central North America on January 1, 1801
February 27, 1801 The District of Columbia was organized. no change to map
April 26, 1802 Georgia ceded its western half, known as the Yazoo Lands, to the federal government. At the same time, the federal government ceded to Georgia the eastern portion of the land previously ceded by South Carolina, though in reality Georgia technically already held title to the land, as the description of the earlier cession was based on an erroneous understanding of geography. Map of the change to the United States in central North America on April 26, 1802
March 1, 1803 The southern half of the Northwest Territory, along with a thin sliver of Indiana Territory, was admitted as the seventeenth state, Ohio. The remainder of the Northwest Territory was transferred to Indiana Territory. The western border was a line due north from the mouth of the Great Miami River; the federal definition of the northern border was a line drawn east from the southern tip of Lake Michigan, whereas the Ohio Constitution stated the line should run from the southern tip of Lake Michigan to the most northerly cape of Maumee Bay, essentially the western tip of Lake Erie. The confusion caused by these varying descriptions of the state's borders, combined with inaccurate knowledge of geography, as no one at the time knew just how far south Lake Michigan extended, would lead to the conflict over the Toledo Strip. Map of the change to the United States in central North America on March 1, 1803
November 3, 1803 The border between Tennessee and Virginia was resurveyed and established, ending the dispute over that part of the border. The border between Kentucky and Tennessee, despite following the original survey, remained vaguely defined. Map of the change to the United States in central North America on November 3, 1803
November 30, 1803 The "Southwick Jog" was transferred from Connecticut to Massachusetts, to put to rest long-standing disagreements over the border between the two states. The final report of the commissioners was delivered this day; it is unclear when the change formally occurred. Map of the change to the United States in central North America on November 30, 1803

1803–1818 (Purchase of Louisiana)

Date Event Change Map
December 20, 1803 The United States purchased Louisiana from France. This is the date of the formal turnover in New Orleans; the purchase was completed on April 30, 1803. The transfer would be recognized in St. Louis in Upper Louisiana on March 10, 1804, known as Three Flags Day.

The acquisition expanded the United States to the whole of the Mississippi River basin, but the extent of what constituted Louisiana in the south was disputed with Spain: the United States claimed the purchase included the part of West Florida west of the Perdido River, whereas Spain claimed it ended at the western border of West Florida; and the southwestern border with New Spain was disputed, as the United States claimed the Sabine River as the border, but Spain maintained it was the Calcasieu River and others.

Map of the change to the United States in central North America on December 20, 1803

Disputes:

Map of the change to the international disputes involving the United States in central North America on December 20, 1803

March 27, 1804 The land between Tennessee and Mississippi Territory previously ceded by Georgia was assigned to Mississippi Territory. Map of the change to the United States in central North America on March 27, 1804
October 1, 1804 Orleans Territory was organized from the Louisiana Purchase south of 33° north, with the remainder being designated the District of Louisiana and placed under the jurisdiction of Indiana Territory. Map of the change to the United States in central North America on October 1, 1804
June 30, 1805 Michigan Territory was organized from Indiana Territory, north of a line east from the southern tip of Lake Michigan, and east of a line north from the lake's northern tip. The southeastern portion of the border technically conflicted with the definition of Ohio, which claimed the Toledo Strip north of that line; however, the exact position of Lake Michigan was not yet known. Map of the change to the United States in central North America on June 30, 1805
July 4, 1805 The District of Louisiana was organized as Louisiana Territory. Map of the change to the United States in central North America on July 4, 1805
March 1, 1809 Illinois Territory was organized from the western half of Indiana Territory. Map of the change to the United States in central North America on March 1, 1809
September 26, 1810 The Republic of West Florida declared independence from Spain, claiming the area of West Florida west of the Perdido River. It maintained some control over its territory. Disputes:
Map of the change to the international disputes involving the United States in central North America on September 26, 1810
December 10, 1810 Armed forces led by William C. C. Claiborne took possession of the portion of West Florida west of the Pearl River, following a proclamation on October 27, 1810, by President James Madison to do so. The United States had considered the region part of the Louisiana Purchase, including the area which had revolted against Spanish Florida and formed the Republic of West Florida. Madison's proclamation stated that it was to be "taken as part" of Orleans Territory. The land west of Mobile Bay to the Pearl River was occupied and annexed de facto by the military in 1811. Disputes:
Map of the change to the international disputes involving the United States in central North America on December 10, 1810
April 30, 1812 Most of Orleans Territory was admitted as the eighteenth state, Louisiana. The southeastern remainder presumably became unorganized territory, as it had no definition for a short time. Map of the change to the United States in central North America on April 30, 1812
May 14, 1812 The claimed portion of West Florida east of the Pearl River was assigned to Mississippi Territory, though the area around Mobile Bay remained under the control of Spanish Florida. The United States militarily occupied Mobile and the surrounding area up to the Perdido River in April 1813. Map of the change to the United States in central North America on May 14, 1812
June 4, 1812 Since its name was now shared with the state of Louisiana, Louisiana Territory was renamed Missouri Territory. Map of the change to the United States in central North America on June 4, 1812
August 4, 1812 The remaining claimed portion of West Florida, west of the Pearl River, was added to Louisiana, following the assent of that state to an act passed by Congress on April 14, 1812. Map of the change to the United States in central North America on August 4, 1812
August 16, 1812 During the War of 1812, the garrison at Fort Detroit surrendered, leading the United Kingdom to occupy Detroit, the capital and population center of Michigan Territory. Disputes:
Map of the change to the disputes involving the United States in central North America on August 16, 1812
September 29, 1813 The British withdrew from Fort Detroit following the Battle of Lake Erie, allowing American forces to regain control over Michigan Territory. Disputes:
Map of the change to the disputes involving the United States in central North America on September 29, 1813
August 24, 1814 British forces capture and burn Washington, but are forced to withdraw the next day. The functions of the capital were only momentarily suspended, though President James Madison took refuge in Brookville, Maryland. no change to map
December 11, 1816 The southern part of Indiana Territory, along with small parts of Illinois Territory and Michigan Territory, were admitted as the nineteenth state, Indiana. The remainder of Indiana Territory across Lake Michigan became unorganized territory. Map of the change to the United States in central North America on December 11, 1816
March 3, 1817 Alabama Territory was organized from the eastern half of Mississippi Territory. Map of the change to the United States in central North America on March 3, 1817
December 10, 1817 Mississippi Territory was admitted as the twentieth state, Mississippi. Map of the change to the United States in central North America on December 10, 1817
February 6, 1818 Alabama Territory created Tuskaloosa County with a description that inadvertently overlapped with Mississippi. It described the border of the county as running "a due west course to, the Tombeckbe river; thence up the same to the Cotton Gin Port". Unknown at the time, the origin of the Tombigbee River and Cotton Gin Port were in Mississippi. Change on paper only:
Map of the change to the United States in central North America on February 6, 1818
June 30, 1818 Per the terms of the Treaty of Ghent ending the War of 1812, the United Kingdom returned Moose Island to Massachusetts, and the United States returned Campobello Island, Deer Island, and Grand Manan Island to the United Kingdom, all of which were captured from the other side during the war. no change to map
December 3, 1818 The half of Illinois Territory south of 42°30′ north was admitted as the twenty-first state, Illinois. The remainder of the territory, along with the unorganized territory that was recently part of Indiana Territory, was assigned to Michigan Territory. Map of the change to the United States in central North America on December 3, 1818

1819–1845 (Northwest expansion)

Date Event Change Map
January 30, 1819 The Treaty of 1818 went into effect, setting 49° north as the border with the United Kingdom west of the Lake of the Woods, and also establishing the Oregon Country as a shared region with the United Kingdom. Oregon Country had no defined northern limit, but it can be assumed that it did not encroach much upon Russian-held lands; this map uses the later-established line at 54°40′ north for simplicity. Map of the change to the United States in central North America on January 30, 1819

Northwestern North America:
Map of the change to the United States in northwest North America on January 30, 1819
July 4, 1819 Arkansaw Territory was organized from the southern slice of Missouri Territory. Map of the change to the United States in central North America on July 4, 1819
December 14, 1819 Alabama Territory was admitted as the twenty-second state, Alabama. The statehood act provided for a survey of the southern part of the border with Mississippi, which was intended to be north–south, for adjustment if it was discovered to encroach upon Mississippi's established counties; it was later discovered to do so. Map of the change to the United States in central North America on December 14, 1819
March 15, 1820 As part of the Missouri Compromise, the District of Maine, the northern and separate part of Massachusetts, was admitted as the twenty-third state, Maine. Map of the change to the United States in central North America on March 15, 1820
April 21, 1820 This is the earliest known date of the name "Arkansas Territory" being officially used instead of "Arkansaw Territory". Map of the change to the United States in central North America on April 21, 1820
May 12, 1820 The border between Kentucky and Tennessee was established. To make up for the fact that the border between the Cumberland Gap and the Tennessee River veered north as much as almost 10 miles from 36°30′ north, a new survey was conducted starting at that latitude on the Mississippi River and moving east to the Tennessee River, hence guaranteeing this last bit of border would fit the original ideal. Map of the change to the United States in central North America on May 12, 1820
July 19, 1820 The overlap of the longitudinal southern border between Alabama and Mississippi was resolved, as per the act admitting Alabama as a state, because the provisional border encroached on Mississippi. As the result of a survey, the southern border terminus was moved about 3.8 miles to the east, which changed the border up to the then-northwest corner of Alabama's Washington County. The date when this happened is unclear; the sources available give either an unpublished report dated May 29, 1820, or the completion of the demarcation of the new line on July 19, 1820. Change on paper only:
Map of the change to the United States in central North Ameirca on July 19, 1820
December 19, 1820 Alabama redefined some county borders, ending its erroneous overlap of Mississippi created on February 6, 1818. Change on paper only:
Map of the change to the United States in central North America on December 19, 1820
February 22, 1821 The Adams–Onís Treaty with Spain took effect. The many changes included: Map of the change to the United States in central North America on February 22, 1821

Disputes:
Map of the change to the international disputes involving the United States in central North America on February 22, 1821
July 10, 1821 East Florida was formally transferred to the United States by Spain. Map of the change to the United States in central North America on July 10, 1821
July 17, 1821 West Florida was formally transferred to the United States by Spain. Map of the change to the United States in central North America on July 17, 1821
August 10, 1821 The southeastern corner of Missouri Territory was admitted as the twenty-fourth state, Missouri, the rest becoming unorganized territory. Map of the change to the United States in central North America on August 10, 1821
March 30, 1822 The former East Florida and West Florida were organized as Florida Territory. Map of the change to the United States in central North America on March 30, 1822
May 26, 1824 The half of Arkansas Territory west of a line south from a point 40 miles west of Missouri's western border was returned to unorganized territory. Map of the change to the United States in central North America on May 26, 1824
January 12, 1825 A treaty with the Russian Empire established 54°40′ north as the northern border of Oregon Country for American purposes; a separate treaty created the same border between Russia and the United Kingdom. As this was likely the de facto border anyway, the region is already mapped with this line. no change to map
May 6, 1828 A treaty with the Cherokee moved the western border of Arkansas Territory, returning part of it to unorganized territory. Map of the change to the United States in central North America on May 6, 1828
January 20, 1831 King William I of the Netherlands, having been asked per the Treaty of Ghent to arbitrate the disputed border between Maine and the United Kingdom, rendered his decision: since reconciling the treaty with the maps given was too difficult, he drew a compromise line. The British government accepted it, but Maine protested, and on January 19, 1832, the American government rejected it. no change to map
July 9, 1832 The region of New Hampshire north of the Connecticut Lakes, which was disputed with the United Kingdom, declared independence as the Republic of Indian Stream. While tiny, it does appear to have maintained some control over its territory. Disputes:
Map of the change to the international disputes involving the United States in central North America on July 9, 1832
June 28, 1834 Michigan Territory gained a large parcel of land from unorganized territory, extending west to the Missouri River and White Earth River. Map of the change to the United States in central North America on June 28, 1834
August 5, 1835 The Republic of Indian Stream recognized the jurisdiction of New Hampshire, thus ending its claimed independence. The date given is of a communication sent to British authorities; other sources note a resolution passed by the citizens of Indian Stream on April 2, 1836. Disputes:
Map of the change to the international disputes involving the United States in central North America on August 5, 1835
June 15, 1836 Arkansas Territory was admitted as the twenty-fifth state, Arkansas. Map of the change to the United States in central North America on June 15, 1836
July 3, 1836 Wisconsin Territory was organized from the western bulk of Michigan Territory. The two large peninsulas between the Great Lakes remained in Michigan Territory; the upper peninsula was included in exchange for the territory abandoning its claim to the Toledo Strip. The territory initially rejected this plan, but would accept it on December 14. Map of the change to the United States in central North America on July 3, 1836
December 14, 1836 Michigan Territory agreed to abandon its claim to the Toledo Strip, ending its dispute with Ohio. Map of the change to the United States in central North America on December 14, 1836
January 26, 1837 Michigan Territory was admitted as the twenty-sixth state, Michigan. Map of the change to the United States in central North America on January 26, 1837
March 28, 1837 The Platte Purchase, obtained from several nations including the Potawatomi, Ioway, Missouria, Otoe, and Sac and Fox, transferred some land from unorganized territory to northwest Missouri, extending its northern border west to the Missouri River. Map of the change to the United States in central North America on March 28, 1837
July 3, 1838 Iowa Territory was organized from Wisconsin Territory west of the Mississippi River. Map of the change to the United States in central North America on July 3, 1838
February 11, 1839 Missouri claimed an area north of its border with Iowa Territory, initiating the long dispute known as the Honey War. Map of the change to the United States in central North America on February 11, 1839
May 21, 1840 Surveying conducted along the border with Texas concluded that the area claimed by Arkansas for Miller County belonged to Texas. Map of the change to the United States in central North America on May 21, 1840
November 10, 1842 The Webster–Ashburton Treaty defined the border with the United Kingdom east of the Rocky Mountains. One source also mentions it very slightly altering the maritime boundary between Michigan and Wisconsin Territory. The treaty resolved the disputes over the northern borders of Maine and New Hampshire, the northeastern border of Wisconsin Territory, and Sugar Island with Michigan.

The border between New York and Vermont on the one side, and the United Kingdom on the other, was clarified by the treaty. In 1816, construction began on an unnamed fort nicknamed "Fort Blunder" on a peninsula in Lake Champlain that, while south of the surveyed border, was discovered to be north of 45° north, which was the border set by the Treaty of Paris and thus in British territory. Consequently, construction on the fort was abandoned. The Webster–Ashburton Treaty specified that section of the border was to follow the surveyed line, rather than the exact parallel, thus moving the fort's area into the United States, and a new fort, Fort Montgomery, would be built on the spot in 1844. As the earlier line was surveyed, even though it did not match the definition, it was deemed to be the legitimate border.

Map of the change to the United States in central North America on November 10, 1842

Disputes:
Map of the change to the international disputes involving the United States in central North America on November 10, 1842
July 5, 1843 Local settlers created a provisional government for Oregon Country. While not official, it did maintain some jurisdiction over the area. Unofficial change: Map of the change to the United States in central North America on July 5, 1843
March 3, 1845 Florida Territory was admitted as the twenty-seventh state, Florida. Map of the change to the United States in central North America on March 3, 1845

1845–1860 (Southwest expansion)

Date Event Change Map
December 29, 1845 The Republic of Texas was annexed and admitted as the twenty-eighth state, Texas, extending the United States southwest to the Rio Grande. All of Texas was claimed by Mexico. While many sources state that Mexico recognized the independence of the eastern portion of Texas, the treaties were rejected by the Mexican government. Texas formally handed over sovereignty to the United States in a ceremony on February 19, 1846. The annexation led to the beginning of the Mexican–American War a few months later. Map of the change to the United States in central North America on December 29, 1845

Disputes:
Map of the change to the international disputes involving the United States in central North America on December 9, 1845
June 15, 1846 The Oregon Treaty established 49° north west of the Lake of the Woods as the continental border (so it did not include Vancouver Island) with land held by the United Kingdom. The sharing of Oregon Country ended, and the United States portion became unorganized territory.

The treaty was vague on which strait should be the border between Vancouver Island and the continent, thus causing a dispute over ownership of the San Juan Islands. It specified "through the middle of the said channel and of Fuca Straits, to the Pacific Ocean".

Map of the change to the United States in central North America on June 15, 1846

Northwestern North America:
Map of the change to the United States in northwest North America on June 15, 1846

Disputes:
Map of the change to the international disputes involving the United States in central North America on June 15, 1846
September 22, 1846 Following the capture on August 18, 1846, of Santa Fe, the capital of the Mexican territory of Santa Fe de Nuevo México, a code of laws known as the Kearny Code was created for the area. The region overlapped with Texas' claim, though Texas had little to no control over the area outside of its eastern quarter. Unofficial change:
Map of the change to the United States in central North America on September 22, 1846
December 28, 1846 The portion of Iowa Territory south of 43°30′ north and east of the Big Sioux River was admitted as the twenty-ninth state, Iowa. The remainder became unorganized territory. Map of the change to the United States in central North America on December 28, 1846
March 13, 1847 The District of Columbia retroceded Alexandria County back to Virginia. Congress passed the act on July 9, 1846, residents of Alexandria County were proclaimed by the president to have agreed to it on September 7, 1846, and Virginia took possession of the land on this date. Map of the change to the United States in central North America on March 13, 1847
May 29, 1848 The southern bulk of Wisconsin Territory was admitted as the thirtieth state, Wisconsin. The remainder became unorganized territory. However, the citizens of the remainder decided to continue on with a civil government, and even elected a delegate to the United States House of Representatives who would be seated on January 15, 1849, essentially making this region a de facto continuation of Wisconsin Territory. Map of the change to the United States in central North America on May 29, 1848
July 4, 1848 The Treaty of Guadalupe Hidalgo ended the Mexican–American War and ceded a large parcel of land from Mexico, consisting of its territories of Alta California and Santa Fe de Nuevo México, and its claim to Texas. A border dispute began over a disagreement about the southern border of Santa Fe de Nuevo México. Map of the change to the United States in central North America on July 4, 1848

Disputes:
Map of the change to the international disputes involving the United States in central North America on July 4, 1848
August 14, 1848 Oregon Territory was organized from the unorganized territory that was formerly part of Oregon Country. Map of the change to the United States in central North America on August 14, 1848
February 13, 1849 The boundary dispute between Iowa and Missouri known as the Honey War was resolved by the Supreme Court of the United States. The resulting border was the Sullivan Line that existed before the dispute, roughly splitting the two claims. Map of the change to the United States in central North America on February 13, 1849
March 3, 1849 Minnesota Territory was organized from the region that had been operating as de facto Wisconsin Territory, and unorganized territory east of the Missouri and White Earth Rivers. Map of the change to the United States in central North America on March 3, 1849
March 12, 1849 A local government formed the State of Deseret and claimed a vast portion of the southwest, including most of the Mexican Cession. Though it petitioned to be admitted to the United States, the proposal was rejected and, in 1850, Utah Territory was formed instead. The claimed area overlapped slightly with Texas' claimed area, as well as part of Oregon Territory. Unofficial change:
Map of the change to the United States in central North America on March 12, 1849
November 24, 1849 Texas, with consent from the United States Congress, extended its border with Louisiana from the west bank of the Sabine River to the middle of the river. no change to map
September 9, 1850 The western portion of the Mexican Cession was admitted as the thirty-first state, California. The portion of the remainder north of 37° north and west of the summit of the Rocky Mountains was organized as Utah Territory. Part of Utah Territory overlapped with the portion of Texas that would be purchased on December 13, 1850, but the law authorizing the purchase was passed on this day, so the borders of Utah Territory assumed that the purchase would go through. Map of the change to the United States in central North America on September 9, 1850
December 9, 1850 The United Kingdom ceded less than one acre of underwater rock for a lighthouse in Lake Erie near Buffalo, New York; although it was on Middle Reef, it was named for the nearby Horseshoe Reef. It was surrounded by British waters, thus creating a form of enclave. Map of the change to the United States in central North America on December 9, 1850
December 13, 1850 The federal government purchased the western claims of Texas. New Mexico Territory was organized from the part of this land east of the Rio Grande, along with the remaining unorganized territory from the Mexican Cession. New Mexico Territory included all of the area that had been governed under the Kearny Code. Map of the change to the United States in central North America on December 13, 1850
April 5, 1851 The State of Deseret dissolved itself, its functions and territory largely having been superseded by Utah Territory. Unofficial change:
Map of the change to the United States in central North America on April 5, 1851
March 2, 1853 Washington Territory was organized from the half of Oregon Territory north of 46° north and the Columbia River. Map of the change to the United States in central North America on March 2, 1853
May 30, 1854 Kansas Territory was organized from unorganized territory north of 37° north, and Nebraska Territory was organized north of 40° north. Much of the remaining unorganized territory, east of 100° west, became known as Indian Territory, designated as a place to resettle Indian tribes.

A small strip between the Texas Panhandle and Kansas Territory was unclaimed because it fell south of Kansas Territory's border but north of 36°30′ north, which had been established in the Missouri Compromise as the northern limit of slavery, and thus Texas could not have it. This became known as the Public Land Strip, or sometimes "No Man's Land".

Map of the change to the United States in central North America on May 30, 1854
June 30, 1854 The United States purchased a large parcel from Mexico known as the Gadsden Purchase, as it offered a much better route for a southern transcontinental railroad. This resolved the border dispute, since the disputed land was included in the purchase. Map of the change to the United States in central North America on June 30, 1854

Disputes:
Map of the change to the international disputes involving the United States in central North America on June 30, 1854
August 4, 1854 The recently obtained Gadsden Purchase was assigned to New Mexico Territory. Map of the change to the United States in central North America on August 4, 1854
January 11, 1855 Boston Corner was transferred from Massachusetts to New York because it was inaccessible from the rest of the Massachusetts. Map of the change to the United States in central North America on January 11, 1855
March 6, 1855 The Supreme Court ruled in favor of Florida in a boundary dispute with Georgia, setting the state boundary line along McNeil's line. no change to map
October 28, 1856 Baker Island and Jarvis Island were claimed under the Guano Islands Act. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on October 28, 1856
May 11, 1858 The eastern half of Minnesota Territory was admitted as the thirty-second state, Minnesota. The remainder became unorganized territory. Map of the change to the United States in central North America on May 11, 1858
August 31, 1858 Navassa Island was claimed under the Guano Islands Act. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on August 31, 1858
December 3, 1858 Howland Island was claimed under the Guano Islands Act. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on December 3, 1859
February 14, 1859 The western half of Oregon Territory was admitted as the thirty-third state, Oregon. The remainder was transferred to Washington Territory. Map of the change to the United States in central North America on February 14, 1859
July 6, 1859 A team of surveyors created the "Middleton Offset", a small notch in the border between Kentucky and Tennessee. It is unknown exactly why this was done, though one theory is a local landowner wanted his property in Tennessee. Map of the change to the United States in central North America on July 6, 1859
September 6, 1859 Johnston Atoll was claimed under the Guano Islands Act, though it had been claimed by Hawaii in 1858. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on September 6, 1859
November 7, 1859 A local government was set up encompassing parts of the territories of Kansas, Nebraska, New Mexico, Utah, and Washington, with the name of Jefferson Territory. While never recognized by the federal government, it generally held control over the area until Colorado Territory was established, which adopted most of its laws. Unofficial change:
Map of the change to the United States in central North America on November 7, 1859
December 27, 1859 Enderbury Island, McKean Island, Phoenix Island, and Starbuck Island were claimed under the Guano Islands Act. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on December 27, 1859
December 29, 1859 Christmas Island and Malden Island were claimed under the Guano Islands Act. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on December 29, 1859
February 8, 1860 Texas created Greer County, claiming part of Indian Territory based on a different understanding from the federal government of which fork of the Red River was the border between the two.

Atafu, Birnie Island, Butaritari, Caroline Island, Fanning Island, Flint Island, Gardner Island, Canton Island, Kingman Reef, Manihiki, Marakei, Nukunono, Palmyra Atoll, Penrhyn, Pukapuka, Rakahanga, Swains Island, Sydney Island, Vostok Island, and Washington Island were all claimed under the Guano Islands Act. Many additional islands were listed as bonded on this date, but based on the coordinates they were either phantoms or duplicates. In addition, Sarah Ann Island was claimed, which may have existed and would be sighted as late as 1917, but has since disappeared.

Map of the change to the United States in central North America on February 8, 1860

Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on February 8, 1860

1860–1865 (Civil War)

Date Event Change Map
December 20, 1860 In response to the election of Abraham Lincoln, South Carolina proclaimed its secession from the Union, withdrawing from the Congress of the United States. Map of the change to the United States in central North America on December 20, 1860

Disputes:
Map of the change to the international disputes involving the United States in central North America on December 20, 1860
January 9, 1861 Mississippi proclaimed its secession from the Union, withdrawing from Congress. Map of the change to the United States in central North America on January 9, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on January 9, 1861
January 10, 1861 Florida proclaimed its secession from the Union, withdrawing from Congress. Map of the change to the United States in central North America on January 10, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on January 10, 1861
January 11, 1861 Alabama proclaimed its secession from the Union, withdrawing from Congress. Map of the change to the United States in central North America on January 11, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on January 11, 1861
January 19, 1861 Georgia proclaimed its secession from the Union, withdrawing from Congress. Map of the change to the United States in central North America on January 19, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on January 19, 1861
January 26, 1861 Louisiana proclaimed its secession from the Union, withdrawing from Congress. However, the 1st and 2nd congressional districts, around New Orleans, maintained representation in Congress. Map of the change to the United States in central North America on January 26, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on January 26, 1861
January 29, 1861 The bulk of Kansas Territory east of 25° west from Washington was admitted as the thirty-fourth state, Kansas. The remainder became unorganized territory. Map of the change to the United States in central North America on January 29, 1861
February 8, 1861 The Confederate States of America was formed by representatives of the seceded states of Alabama, Georgia, Florida, Louisiana, Mississippi, and South Carolina. Disputes:
Map of the change to the international disputes involving the United States in central North America on February 8, 1861
February 28, 1861 Colorado Territory was organized from portions of Nebraska Territory, New Mexico Territory, and Utah Territory, along with unorganized territory. Map of the change to the United States in central North America on February 28, 1861
March 2, 1861 Texas proclaimed its secession from the Union and was admitted to the Confederate States, withdrawing from Congress.

Dakota Territory was organized from Nebraska Territory and the unorganized territory north of it. Nebraska Territory's western border was moved to 33° west from Washington, gaining small portions of Utah Territory and Washington Territory. Nevada Territory was organized from Utah Territory west of 39° west from Washington.

Map of the change to the United States in central North America on March 2, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on March 2, 1861
March 28, 1861 Representatives in the southern half of New Mexico Territory proclaimed an independent Arizona Territory south of 34° north. Disputes:
Map of the change to the international disputes involving the United States in central North America on March 28, 1861
April 17, 1861 Following the Battle of Fort Sumter and President Abraham Lincoln's call for troops to respond, Virginia proclaimed its secession from the Union, withdrawing from Congress. However, the 1st (along the Eastern Shore), 7th (near Washington, D.C.), and 10th, 11th, and 12th (in the northwest of the state) congressional districts maintained representation in Congress. Map of the change to the United States in central North America on April 17, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on April 17, 1861
May 6, 1861 Arkansas proclaimed its secession from the Union, withdrawing from Congress. Map of the change to the United States in central North America on May 6, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on May 6, 1861
May 7, 1861 Virginia was admitted to the Confederate States. Disputes:
Map of the change to the international disputes involving the United States in central North America on May 7, 1861
May 16, 1861 Kentucky declared itself neutral in the American Civil War. no change to map
May 20, 1861 Arkansas was admitted to the Confederate States.

North Carolina proclaimed its secession from the Union, withdrawing from Congress.

Map of the change to the United States in central North America on May 20, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on May 20, 1861
May 21, 1861 North Carolina was admitted to the Confederate States. The law admitting the state required a presidential proclamation before it was to take effect, which sources say took place on this date; the only primary source found so far is a statement from Jefferson Davis on July 20 stating that the proclamation had been made. Disputes:
Map of the change to the international disputes involving the United States in central North America on May 21, 1861
June 6, 1861 Robert Williamson Steele, governor of Jefferson Territory, declared the territory disbanded and handed over the government to the first governor of Colorado Territory. Unofficial change:
Map of the change to the United States in central North America on June 6, 1861
June 8, 1861 Tennessee proclaimed its secession from the Union, withdrawing from Congress. However, the 2nd, 3rd, and 4th congressional districts in the central part of the state maintained representation in Congress. Map of the change to the United States in central North America on June 8, 1861

Disputes:
Map of the change to the international disputes involving the United States in central North America on June 8, 1861
June 25, 1861 The federal government recognized the Restored Government of Virginia in Wheeling as the legitimate government of Virginia. Map of the change to the United States in central North America on June 25, 1861
July 2, 1861 Tennessee was admitted to the Confederate States. Disputes:
Map of the change to the international disputes involving the United States in central North America on July 2, 1861
August 1, 1861 Following Confederate victory in the First Battle of Mesilla, Arizona Territory was proclaimed as part of the Confederate States. Disputes:
Map of the change to the international disputes involving the United States in central North America on August 1, 1861
September 13, 1861 Following the Confederate occupation of Columbus, Kentucky, on September 3, 1861, the state abandoned neutrality and aligned with the Union government. no change to map
October 31, 1861 A splinter government in Neosho, Missouri, proclaimed the secession of the state from the United States. Disputes:
Map of the change to the international disputes involving the United States in central North America on October 31, 1861
November 20, 1861 A convention in Russellville, Kentucky, proclaimed the formation of a splinter government in Bowling Green and the secession of Kentucky from the United States. Disputes:
Map of the change to the international disputes involving the United States in central North America on November 20, 1861
November 28, 1861 The splinter Neosho government of Missouri was admitted to the Confederate States. The Confederate States never held much power over the state, but it was given full representation in the legislature. Disputes:
Map of the change to the international disputes involving the United States in central North America on November 28, 1861
December 10, 1861 The splinter Bowling Green government of Kentucky was admitted to the Confederate States. The Confederate States never held much power over the state, but it was given full representation in the legislature. Disputes:
Map of the change to the international disputes involving the United States in central North America on December 10, 1861
December 21, 1861 The Confederate States ratified treaties with the Osage, and the Seneca and Shawnee. Disputes:
Map of the change to the international disputes involving the United States in central North America on December 21, 1861
December 23, 1861 The Confederate States ratified treaties with the Cherokee, granting them a delegate to the Congress of the Confederate States, and with the Seminole, granting them a delegate to be shared with the Creek. Disputes:
Map of the change to the international disputes involving the United States in central North America on December 23, 1861
December 31, 1861 The Confederate States ratified treaties with the Choctaw and Chickasaw, granting them a delegate in the Congress of the Confederate States; with the Comanche; with the Creek, granting them a delegate to be shared with the Seminole; and the Quapaw. Disputes:
Map of the change to the international disputes involving the United States in central North America on December 31, 1861
March 1, 1862 A decree by the Supreme Court of the United States took effect, modifying the border between Massachusetts and Rhode Island. Map of the change to the United States in central North America on March 1, 1862
April 15, 1862 Palmyra Atoll was annexed by Hawaii, and the American claim falls dormant. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on April 15, 1862
July 14, 1862 The slice of Utah Territory west of 38° west from Washington was transferred to Nevada Territory. Map of the change to the United States in central North America on July 14, 1862
December 30, 1862 The Swan Islands were claimed under the Guano Islands Act. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on December 30, 1862
February 24, 1863 Arizona Territory was organized from the half of New Mexico Territory west of 32° west from Washington. Map of the change to the United States in central North America on February 24, 1863
March 3, 1863 Idaho Territory was organized from the parts of Dakota Territory and Nebraska Territory west of 27° west from Washington, and the half of Washington Territory east of the Snake River and a line north from the mouth of the Clearwater River. Map of the change to the United States in central North America on March 3, 1863
March 4, 1863 Because of a disruption in voting and low turnout, no one was allowed to take the seats in the United States House of Representatives held by the Unionist areas of Louisiana, Tennessee, and Virginia, effectively expelling the states. Map of the change to the United States in central North America on March 4, 1863
June 20, 1863 The northwestern counties of Virginia, represented by the Restored Government of Virginia in Wheeling, were split from the rest of Virginia and admitted to the Union as the thirty-fifth state, West Virginia. The Restored Government of Virginia was relocated to Alexandria. Map of the change to the United States in central North America on June 20, 1863
August 5, 1863 Berkeley County was transferred by the federal government from Virginia to West Virginia. Map of the change to the United States in central North America on August 5, 1863
November 2, 1863 Jefferson County was transferred from Virginia to West Virginia. Map of the change to the United States in central North America on November 2, 1863
May 26, 1864 Montana Territory was organized from the northeast third of Idaho Territory, and the southeast third of Idaho Territory was transferred to Dakota Territory. Map of the change to the United States in central North America on May 26, 1864
October 15, 1864 Malden Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on October 15, 1864
October 31, 1864 Nevada Territory was admitted as the thirty-sixth state, Nevada. Map of the change to the United States in central North America on October 31, 1864
May 5, 1865 The Confederate States cabinet met in Washington, Georgia, and dissolved. Military surrenders were scattered throughout 1865, but the most important is regarded as that of the Army of Northern Virginia following the Battle of Appomattox Court House on April 9. Disputes:
Map of the change to the international disputes involving the United States in central North America on May 5, 1865

1866–1897 (Reconstruction and western statehood)

Date Event Change Map
May 5, 1866 The slice of Utah Territory west of 37° west from Washington was transferred to Nevada. Map of the change to the United States in central North America on May 5, 1866
July 24, 1866 Tennessee was readmitted to Congress. Map of the change to the United States in central North America on July 24, 1866
December 26, 1866 Starbuck Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on December 26, 1866
January 18, 1867 The northwestern corner of Arizona Territory, west of the Colorado River and 37° west from Washington, was transferred to Nevada. The law transferring the land was approved May 5, 1866, but unlike the Utah Territory transfer of that day, this transfer was contingent on the state accepting it. Map of the change to the United States in central North America on January 18, 1867
March 1, 1867 Nebraska Territory was admitted as the thirty-seventh state, Nebraska. Map of the change to the United States in central North America on March 1, 1867
July 1, 1867 Canada was formed from several British colonies, including New Brunswick, thus inheriting the dispute over Machias Seal Island and North Rock. Disputes:
Map of the change to the international disputes involving the United States in central North America on July 1, 1867
August 28, 1867 Midway Atoll was claimed. An attempt had been made at the time of its discovery in 1859 to claim it under the Guano Islands Act. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 28, 1867
October 18, 1867 Alaska was purchased from the Russian Empire and designated the Department of Alaska. A vague description and lack of quality surveying made the southeastern border with British holdings unclear and disputed. Northwestern North America:
Map of the change to the United States in northwest North America on October 18, 1867
June 22, 1868 Arkansas was readmitted to Congress. Map of the change to the United States in central North America on June 22, 1868
June 25, 1868 Florida was readmitted to Congress. Map of the change to the United States in central North America on June 25, 1868
July 4, 1868 North Carolina was readmitted to Congress. Map of the change to the United States in central North America on July 4, 1868
July 9, 1868 Louisiana and South Carolina were readmitted to Congress.

Caroline Island was claimed by the United Kingdom.

Map of the change to the United States in central North America on July 9, 1868

Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on July 9, 1868
July 13, 1868 Alabama was readmitted to Congress. Map of the change to the United States in central North America on July 13, 1868
July 25, 1868 Georgia was readmitted to Congress.

Wyoming Territory was organized from portions of Dakota, Idaho, and Utah Territories. The territory would remain under the jurisdiction of the Dakota Territory until its own government was organized on May 19, 1869. The act organizing Wyoming Territory became law on this date, but it is unclear if the territory could be considered "organized" until May 19, 1869, as the act specifies it was not to take effect until a government is organized; however, all sources use this date as the creation, and most use it for the organization, of the territory. A tiny portion of the Dakota Territory was erroneously left behind on the western side of Wyoming Territory.

Map of the change to the United States in central North America on July 25, 1868
August 12, 1868 The list of bonded guano island claims mentions "Islands in Caribbean Sea not named" bonded on this date, but it is unknown to what this is referring. no change to map
December 11, 1868 Serrana Bank was claimed under the Guano Islands Act. Colombia has claimed it throughout its history. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on December 11, 1868
March 3, 1869 Georgia was again expelled from Congress following failures of Reconstruction in the state. Map of the change to the United States in central North America on March 3, 1869
November 22, 1869 Bajo Nuevo Bank, Pedro Cays, Quita Sueño Bank, and Roncador Bank were claimed under the Guano Islands Act. Except for Pedro Cays, Colombia has claimed them throughout its history. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on November 22, 1869
January 26, 1870 Virginia was readmitted to Congress. Map of the change to the United States in central North America on January 26, 1870
February 23, 1870 Mississippi was readmitted to Congress. Map of the change to the United States in central North America on February 23, 1870
March 30, 1870 Texas was readmitted to Congress. Map of the change to the United States in central North America on March 30, 1870
July 15, 1870 Georgia was again readmitted to Congress.

The North-Western Territory was transferred by the United Kingdom to Canada, thus transferring its portion of the Alaska boundary dispute.

Map of the change to the United States in central North America on July 15, 1870

Northwestern North America:
Map of the change to the United States in northwest North America on July 15, 1870
February 9, 1871 A small parcel was transferred from Dakota Territory to Nebraska following a sudden change in course of the Missouri River. Map of the change to the United States in central North America on February 9, 1871
July 20, 1871 British Columbia joined Canada, transferring the dispute over the San Juan Islands as well as its portion of the Alaska boundary dispute. Disputes:
Map of the change to the international disputes involving the United States in central North America on July 20, 1871

Northwestern North America:
Map of the change to the United States in northwest North America on July 20, 1871
October 21, 1872 The dispute with Canada over the San Juan Islands was resolved in the favor of the United States claim. Disputes:
Map of the change to the international disputes involving the United States in central North America on October 21, 1872
1873 Vostok Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean sometime in 1873
February 17, 1873 The small portion of Dakota Territory that was left behind when Wyoming Territory was created was transferred to Montana Territory. Map of the change to the United States in Central North America on February 17, 1873
August 1, 1876 Colorado Territory was admitted as the thirty-eighth state, Colorado. Map of the change to the United States in central North America on August 1, 1876
August 13, 1877 The United Kingdom created the British Western Pacific Territories, including Atafu and Nukunono. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 13, 1877
March 3, 1879 The border across the Chesapeake Bay between Maryland and Virginia was decided via arbitration. It is unknown if any land actually changed hands. too vague to map
September 8, 1879 Arenas Key, claimed by Mexico; the Morant Cays; and Serranilla Bank, claimed by Colombia, were claimed by the United States under the Guano Islands Act; according to the Office of Insular Affairs, Serranilla Bank was claimed again on September 13, 1880. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on September 8, 1879
April 7, 1880 A very small area of Fair Haven, Vermont, was transferred to New York in response to a change in the course in the Poultney River. too small to map
September 13, 1880 Western Triangle Island, claimed by Mexico, was claimed by the United States under the Guano Islands Act. The list of bonded claims also mentions a "De Anes" island claimed on this date, with coordinates matching Isla de Aves; however, the same list points out that the claim to "Aves Island" was found to be invalid. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on September 13, 1880
1881 Flint Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean sometime in 1881
May 23, 1882 The area between 43° north and the Keya Paha and Niobrara Rivers was transferred from Dakota Territory to Nebraska. The act was passed in Congress on March 28 and accepted by the Nebraska legislature on this date. Map of the change to the United States in central North America on May 23, 1882
June 1, 1882 The Morant Cays and Pedro Cays were annexed by the United Kingdom to Jamaica; it appears they were no longer claimed by the United States after this. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on June 1, 1882
May 17, 1884 The Department of Alaska was organized into the District of Alaska. Northwestern North America:
Map of the change to the United States in northwest North America on May 17, 1884
June 21, 1884 The Alacrans Islands, claimed by Mexico, were claimed under the Guano Islands Act. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on June 21, 1884
March 15, 1888 Fanning Island was annexed by the United Kingdom; it appears the island was no longer claimed by the United States after this. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on March 15, 1888
March 17, 1888 Christmas Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on March 17, 1888
October 26, 1888 The Cook Islands became a protectorate of the United Kingdom, thus initiating a claim on the atolls of Manihiki, Penrhyn, Pukapuka, and Rakahanga. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on October 26, 1888
May 29, 1889 Washington Island was annexed by the United Kingdom; it appears the island was no longer claimed by the United States after this. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on May 29, 1889
June 3, 1889 Jarvis Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on June 3, 1889
June 26, 1889 Sydney Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on June 26, 1889
June 29, 1889 Phoenix Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on June 29, 1889
July 10, 1889 Birnie Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on July 10, 1889
November 2, 1889 Dakota Territory was split in half along the "seventh standard parallel north", a few miles south of 46° north, and admitted as the thirty-ninth state, North Dakota, and the fortieth state, South Dakota. Map of the change to the United States in central North America on November 2, 1889
November 8, 1889 Montana Territory was admitted as the forty-first state, Montana. Map of the change to the United States in central North America on November 8, 1889
November 11, 1889 Washington Territory was admitted as the forty-second state, Washington. Map of the change to the United States in central North America on November 11, 1889
May 2, 1890 Oklahoma Territory was organized from the Public Land Strip and the western half of Indian Territory, except for the Cherokee Outlet, which would be added later upon cession from the Cherokee. Map of the change to the United States in central North America on May 2, 1890
July 3, 1890 Idaho Territory was admitted as the forty-third state, Idaho. Map of the change to the United States in central North America on July 3, 1890
July 10, 1890 Wyoming Territory was admitted as the forty-fourth state, Wyoming. Map of the change to the United States in central North America on July 10, 1890
March 8, 1892 The Gilbert Islands became a protectorate of the United Kingdom, thus initiating a claim on Butaritari and Marakei. No record of a United States claim exists after this point, so it is assumed this is when the claim fell dormant. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on March 8, 1892
May 28, 1892 Gardner Island was claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on May 28, 1892
September 16, 1893 Per a treaty with the Cherokee, the federal government purchased the Cherokee Outlet in the Indian Territory and opened it to settlement, transferring it to Oklahoma Territory as provided in the Oklahoma Organic Act. Map of the change to the United States in central North America on September 16, 1893
November 17, 1894 The Alacrans Islands, Arenas Key, and Western Triangle Island were stricken from the list of claimed guano islands. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on November 17, 1894
January 4, 1896 Utah Territory was admitted as the forty-fifth state, Utah. Map of the change to the United States in central North America on January 4, 1896
March 16, 1896 The dispute between the federal government, on behalf of Oklahoma Territory, and Texas over Greer County was resolved in favor of the federal claim. Map of the change to the United States in central North America on March 16, 1896
July 24, 1897 To account for an earlier shift in the course of the Missouri River, an island was transferred from Nebraska to South Dakota. Map of the change to the United States in central North America on July 24, 1897

1898–1945 (Pacific and Caribbean expansion)

Date Event Change Map
August 12, 1898 The Republic of Hawaii was annexed. The ceremony to transfer sovereignty occurred on this date; the act was signed on July 7, 1898. Johnston Atoll was not included with Hawaii, nor was Sikaiana Atoll, which had been ceded to Hawaii in 1856 by its residents and approved by King Kamehameha IV. However, the annexation was based on the islands named in a report of the Hawaiian Commission, which omitted Sikaiana. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 12, 1898
January 17, 1899 Wake Island was claimed. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on January 17, 1899
April 11, 1899 Guam, Porto Rico, and, on agreed payment of $20 million, the Philippines were ceded by Spain following the Spanish–American War. The Philippines were claimed by the First Philippine Republic. The ceded region for the Philippines included the island of Palmas, which was administered by the Netherlands. This overlap would not be noticed until January 21, 1906. While the United States occupied Cuba for a time, it was not ceded nor claimed. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on April 11, 1899

Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on April 11, 1899
February 16, 1900 The United States took ownership of the Samoan Islands east of 171° west, per the terms of the Tripartite Convention. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on February 16, 1900
February 19, 1900 The newly acquired Samoan islands were established as Naval Station, Tutuila. It included all of the islands granted by the Tripartite Convention, though formal cession of the islands by local authorities would take place later in 1900 and 1904. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on February 19, 1900
April 12, 1900 Porto Rico was organized into a civil territory. no change to map
April 17, 1900 The island of Tutuila was formally ceded to the United States and added to Naval Station, Tutuila. As the United States had already claimed the island on February 19, 1900, no change is mapped. The treaty would be ratified by Congress on February 20, 1929.
June 14, 1900 The former Republic of Hawaii was organized into Hawaii Territory. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on June 14, 1900
March 3, 1901 The transfer for a thin sliver of Bristol, Tennessee, to Bristol, Virginia, was approved by Congress after having been approved by both states. The location of the border along Main Street (now State Street) between the two cities was either the northern sidewalk of the street, or down the middle of the street; Tennessee's cession of the northern half of the street laid the issue to rest. too small to map
March 23, 1901 The president of the First Philippine Republic, Emilio Aguinaldo, was captured, and the republic was dissolved.

On this same date several islands, Cagayan de Sulu and Sibutu among them, were purchased from Spain and assigned to the Philippines, which was then being governed as a U.S. insular area. The borders specified in the Treaty of Paris of 1898 had excluded these islands; the new treaty simply ceded "any and all islands belonging to the Philippine Archipelago".

Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on March 23, 1901
July 4, 1901 The Insular Government of the Philippine Islands was established. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on July 4, 1901
July 1, 1902 The Philippines were organized. no change to map
October 20, 1903 The Alaska boundary dispute with Canada was resolved, generally in favor of the United States claim. Northwestern North America:
Map of the change to the United States in northwest North America on October 20, 1903
December 10, 1903 Land along southern Guantánamo Bay was leased in perpetuity from Cuba for use as a naval base; the treaty took effect February 23, 1903, and the formal handover occurred on this date. no change to map
May 4, 1904 The United States took ownership of the Panama Canal Zone. At this stage, only the most basic borders were defined; it was a zone surrounding the canal on each side for five miles, but excluded the cities of Colón and Panama City, which remained exclaves of Panama, as well as the water for their harbors. The Hay–Bunau-Varilla Treaty granting it to the United States was ratified on February 26, 1904. A formal border agreement, which also gave the Canal Zone some land and a lighthouse in northwest Colón, would be ratified on June 15, 1904. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on May 4, 1904
July 16, 1904 The Manuʻa islands were formally ceded to the United States and added to Naval Station, Tutuila. As the United States had already claimed the islands on February 19, 1900, no change is mapped. The treaty would be ratified by Congress on February 20, 1929. no change to map
December 12, 1904 The "Taft Agreement" was made with Panama on December 3, with one of its sections refining the maritime boundary of the harbor of Panama City and the Panama Canal Zone. It became effective December 12.
February 10, 1905 The border between Arkansas and Indian Territory was slightly adjusted near Fort Smith, Arkansas, transferring a small amount of land on the east side of the Poteau River to Arkansas. Map of the change to the United States in central North America on February 10, 1905
September 26, 1907 New Zealand became largely independent from the United Kingdom, inheriting the claim on the atolls of Manihiki, Penrhyn, Pukapuka, and Rakahanga. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on September 26, 1907
November 16, 1907 Indian Territory and Oklahoma Territory were combined and admitted as the forty-sixth state, Oklahoma. Map of the change to the United States in central North America on November 16, 1907
April 11, 1908 A boundary treaty with the United Kingdom on behalf of Canada redefined the maritime borders between the United States and Canada. Among other changes, this "de-enclaved" Horseshoe Reef Lighthouse in Lake Erie by making the water around it contiguous with the water on the American side of the border. no change to map
January 1, 1909 The new Constitution of Michigan included some area of Wisconsin within its definition of Michigan. Map of the change to the United States in central North America on January 1, 1909
August 20, 1910 A boundary treaty with the United Kingdom on behalf of Canada addressed a slight uncertainty in the maritime border in Passamaquoddy Bay between Maine and Canada. The border was adjusted to run east of Pope's Folly Island, which previously lay on the border line, and had been the subject of some debate for many years. Map of the change to the United States in central North America on August 20, 1910
July 17, 1911 Naval Station, Tutuila, was renamed American Samoa; the station continued to operate separate from territorial governance until 1951. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on July 17, 1911
January 6, 1912 New Mexico Territory was admitted as the forty-seventh state, New Mexico. Map of the change to the United States in central North America on January 6, 1912
February 14, 1912 Arizona Territory was admitted as the forty-eighth state, Arizona. Map of the change to the United States in central North America on February 14, 1912
August 24, 1912 The District of Alaska was reorganized as the Alaska Territory. Northwestern North America:
Map of the change to the United States in northwest North America on August 24, 1912
January 31, 1913 New Mexico filed suit in the Supreme Court against Texas over the "Country Club Dispute", questioning whether the present course or the 1850 course of the Rio Grande should be their border. Map of the change to the United States in central North America on January 31, 1913
August 5, 1914 The Corn Islands were leased from Nicaragua for a period of 99 years; however, this was not a full transfer of sovereignty, and the islands were never administered as an insular area. no change to map
May 1, 1915 The borders of the Panama Canal Zone were explicitly defined. Whereas the original definition was a simple corridor surrounding the canal, this treaty specified the actual border. Among the changes this caused were: a slice of Canal Zone was ceded to Panama so Panama City would be connected with the rest of the country; the middle island of the Las Tres Hermanas Islands, which marked the border of Panama City's harbor, was wholly made part of Canal Zone; Gatun Lake and other surrounding waters were formally annexed to the territory; and an area of northwest Colón was ceded to Canal Zone. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on May 1, 1915
May 27, 1915 Under Article II of the 1903 Treaty, the United States expropriated from Panama several areas around the mouth of the Rio Chagres, annexing them to the Panama Canal Zone. too small to map
December 8, 1915 The United States expropriated from Panama a triangle of land, which included the historic Fort San Lorenzo, between the Rio Chagres, Caribbean Sea and the Panama Canal Zone, to which it was annexed.
January 17, 1916 Navassa Island was formally claimed for lighthouse purposes. no change to map
August 29, 1916 The Philippines were reorganized to provide more autonomous government.
March 31, 1917 The Danish Virgin Islands were purchased from Denmark and renamed the United States Virgin Islands. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on March 31, 1917
July 12, 1918 The United States expropriated from Panama 2.6 hectares of land at Punta Paitilla in Panama City and annexed it to the Panama Canal Zone. That area was enlarged to about 50 hectares within several months. too small to map
August 21, 1918 The United States expropriated from Panama land between the Rio Chagres and the Quebrada Majagual and annexed it to the Panama Canal Zone. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on August 21, 1918
September 13, 1918 Minnesota and Wisconsin exchanged islands in the Mississippi River: Island Seventytwo was transferred to Winona, Minnesota, and Barron's Island was transferred to La Crosse, Wisconsin. Map of the change to the United States in central North America on September 13, 1918
September 18, 1919 The island of Largo Remo was annexed to the Panama Canal Zone under the United States right of expropriation in the 1903 Canal Treaty. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on September 18, 1919
June 16, 1920 Fifteen hectares on the island of Taboga Island were annexed to the Panama Canal Zone. too small to map
June 30, 1921 The "Wedge" dispute between Delaware and Pennsylvania was resolved in Delaware's favor. The disputed land had generally been administered by Delaware, even electing a member of the Delaware legislature in the mid-19th century, but federal maps had included the land as part of Pennsylvania at least as late as 1900. The states had agreed on a resolution, and it was affirmed by an act of Congress on this date. Some sources, both contemporary and modern, note that, in the original process of resurveying the border in 1892, a very thin, horn-shaped region along the arc was transferred from Delaware to Pennsylvania; however, no federal maps found reflect this, and it is unclear if this transfer actually occurred. Map of the change to the United States in central North America on June 30, 1921
May 10, 1922 Kingman Reef was formally annexed. no change to map
October 8, 1923 Michigan expanded its claim to Wisconsin territory, though Wisconsin never lost control over the area. Map of the change to the United States in central North America on October 8, 1923
November 15, 1923 The Swan Islands were claimed by Honduras. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on November 15, 1923
February 1, 1924 The future area for Madden Lake was annexed to the Panama Canal Zone under the United States right of expropriation in the 1903 Canal Treaty. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on February 1, 1924
March 4, 1925 Swains Island was added to American Samoa. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on March 4, 1925
July 17, 1925 The border with Canada was adjusted in several places. The only change to a land border redefined how the border between the Lake of the Woods and the Rocky Mountains should be considered; previously, the border followed the curve of the parallel between each border monument, while the treaty changed this to straight lines between each monument. Through this, the United States netted a gain of between 30 and 35 acres of land. Because of the extremely small shift, the lack of specific documentation of where the changes occurred, and the lack of any human impact, this change is not mapped. There was also a change to the border in the Lake of the Woods; a surveying anomaly caused the previous border to intersect itself several times in the lake, creating enclaves of United States water surrounded by Canadian water. The treaty changed the border to use the southernmost intersection as the northwestern point of the Lake of the Woods. Finally, the maritime border in the Bay of Fundy was adjusted, netting Canada roughly 9 acres of water. too small to map
March 1, 1926 The Supreme Court of the United States resolved the conflict between Michigan and Wisconsin in the favor of Wisconsin. Map of the change to the United States in central North America on March 1, 1926
July 29, 1926 Johnston Atoll was established as a federal bird refuge and placed under the jurisdiction of the United States Department of Agriculture. The atoll had originally been claimed by both the United States and Hawaii in 1858, but little activity apart from guano mining had taken place, and it had been largely abandoned for decades. no change to map
November 22, 1926 The Supreme Court of the United States defined the border between Michigan and Wisconsin, transferring all islands south of the Quinnesec Falls on the Menominee River to Wisconsin, and all islands north of the falls to Michigan; it is unknown specifically which islands were transferred in this fashion. However, an error in the border description introduced a small overlap between the two states over several islands in Lake Michigan north of the Door Peninsula. Map of the change to the United States in central North America on November 22, 1926
July 18, 1927 The United States expropriated from Panama another 33 hectares of land on the islands of Taboga and Taboguilla and annexed them to the Panama Canal Zone. too small to map
October 26, 1927 Two bancos along the Colorado River were ceded from Mexico to Arizona.
December 5, 1927 The "Country Club Dispute" between New Mexico and Texas was resolved in Texas's favor. Map of the change to the United States in Central North America on December 5, 1927
April 4, 1928 The Island of Palmas Case was decided in the favor of the Netherlands, ceding Palmas to the Dutch East Indies. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on April 4, 1928
September 24, 1928 The United States expropriated from Panama three hectares of land at El Cerro de Doscientos Pies ("200-Foot Hill") near Las Minas Bay and annexed it to the Panama Canal Zone. too small to map
July 22, 1930 The United States expropriated from Panama 25 hectares on Jicarita Island and 60 hectares at Punta Morro de Puercos and annexed them to the Panama Canal Zone.
April 15, 1931 The United States expropriated from Panama additional areas around the soon-to-be-built Madden Dam and annexed them to the Panama Canal Zone. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on April 15, 1931
May 3, 1932 The United States adjusted the border at Punta Paitilla in the Canal Zone, returning a small amount of land to Panama. This was the site for a planned new American embassy, which had to be built on foreign soil. too small to map
May 17, 1932 Porto Rico was renamed Puerto Rico. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on May 17, 1932
December 13, 1932 The Mangsee Islands and seven of the Turtle Islands were ceded by the United Kingdom from North Borneo to the Philippines. The islands were supposed to be included in the 1900 transfer of islands from Spain to the United States. Per the terms of the treaty, the United Kingdom continued to administer the islands until requested, and, after the Philippines' independence, the Philippine government made such a request and took control. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on December 13, 1932
May 29, 1933 The Supreme Court of the United States ruled that the border between New Hampshire and Vermont was the low water mark of the west bank of the Connecticut River; Vermont had sought to have the border placed in the middle of the river. no change to map
November 13, 1933 A treaty created the Rio Grande Rectification Project, which, from 1935 to 1938, straightened and stabilized the path of the Rio Grande through the El Paso–Juárez Valley. By the end of the project, 174 parcels had been transferred between Mexico and Texas, each side receiving an equal area of land. too small to map
December 29, 1934 Kingman Reef was placed under the jurisdiction of the United States Department of the Navy. no change to map
November 15, 1935 The Insular Government of the Philippine Islands was dissolved and replaced with the Commonwealth of the Philippines. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on November 15, 1935
March 16, 1936 The de jure overlap between Michigan and Wisconsin was resolved by the Supreme Court of the United States. Map of the change to the United States in central North America on March 16, 1936
May 13, 1936 Baker Island, Howland Island, and Jarvis Island were formally annexed and placed under the jurisdiction of the United States Department of the Interior, ending the United Kingdom's claim to Jarvis Island. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on May 13, 1936
June 22, 1936 The U.S. Virgin Islands were organized into a civil territory. no change to map
August 6, 1936 Canton Island, Enderbury Island, and McKean Island were claimed by the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 6, 1936
April 6, 1939 The condominium of the Canton and Enderbury Islands was established with the United Kingdom. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on April 6, 1939
July 27, 1939 Panama gained a sovereign corridor that was carved out of the Panama Canal Zone connecting Colón with the rest of Panama, along with a three-dimensional "tube" of sovereignty for a future crossing over an American highway. A corridor consisting of the road from the Canal Zone boundary to Madden Dam was annexed to the Canal Zone. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on July 27, 1939
August 16, 1939 This is the earliest date so far discovered for when the United States began claiming Fakaofo, Funafuti, Hull Island, Niulakita, Nukufetau, and Nukulaelae. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 16, 1939
December 10, 1941 Governor George McMillin surrendered Guam to the Japanese military. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on December 10, 1941
December 23, 1941 The garrison on Wake Island surrendered to the Japanese military. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on December 23, 1941
March 26, 1942 The government of the Philippines evacuated from the territory in the face of Japanese advance. A government-in-exile would be established in Washington, D.C., on May 17, 1942. The United States Army Forces in the Far East would surrender on April 9, 1942, following the Battle of Bataan, and the final military holdouts would surrender on May 6, 1942, following the Battle of Corregidor. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on March 26, 1942
October 14, 1943 The Second Philippine Republic was established as a puppet state of Japan. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on October 14, 1943
August 10, 1944 Guam was captured from Japan. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 10, 1944
August 17, 1945 The Second Philippine Republic, in exile in Tokyo since April 3, 1945, was dissolved. The process of re-establishing the Commonwealth government on Philippine soil had started on October 23, 1944. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 17, 1945
September 4, 1945 The Japanese garrison on Wake Island surrendered to the United States. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on September 4, 1945

1946–present (Decolonization)

Date Event Change map
July 4, 1946 The Commonwealth of the Philippines became independent as the Republic of the Philippines. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on July 4, 1946
July 18, 1947 The United Nations entrusted the Trust Territory of the Pacific Islands to the United States. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on July 18, 1947
January 1, 1949 The Tokelau Islands were incorporated into New Zealand, which inherited the claims on Atafu, Fakaofo, and Nukunono. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on January 1, 1949
August 1, 1950 Guam was organized into a civil territory. no change to map
August 3, 1950 Kansas and Missouri exchanged small portions of land along the Missouri River, to accord with shifts in the river following a flood in 1944. Map of the change to the United States in central North America on August 3, 1950
May 6, 1954 Alabama and Florida defined their border around the mouth of the Perdido River. not mapped
April 11, 1955 Panama's corridor connecting Colón with the rest of Panama was realigned within the Panama Canal Zone. Several three-dimensional "tubes" of sovereignty were also created, allowing Panamanian bridges to pass over rivers and a highway at several locations within the Canal Zone. too small to map
August 23, 1955 Several border locations of the Panama Canal Zone were redefined. Punta Paitilla, the land held on Taboga Island, and the remaining American holdings in Colón and Panama City were ceded to Panama. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on August 23, 1955
January 3, 1959 The Alaska Territory was admitted as the forty-ninth state, Alaska. Northwestern North America:
Map of the change to the United States in northwest North America on January 3, 1959
August 21, 1959 Most of Hawaii Territory was admitted as the fiftieth state, Hawaii. Palmyra Atoll was excluded from statehood and remained a territory. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 21, 1959
August 25, 1961 About 20 acres of land was transferred from Minnesota to North Dakota near Fargo, North Dakota. too small to map
January 14, 1964 The Chamizal, a tract of land between El Paso, Texas, and Ciudad Juárez, Chihuahua, was divided between the United States and Mexico. Map of the change to the United States in central North America on January 14, 1964
August 4, 1965 The Cook Islands became self-governing from New Zealand. It claimed the atolls of Manihiki, Penrhyn, Pukapuka, and Rakahanga. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on August 4, 1965
December 30, 1966 Land on Diego Garcia in the Indian Ocean was leased from the United Kingdom for use as a military base. no change to map
April 25, 1971 The lease of the Corn Islands from Nicaragua was terminated.
September 1, 1972 The United States recognized the sovereignty of Honduras over the Swan Islands. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on September 1, 1972
March 1, 1977 The United States claimed maritime borders west of the Strait of Juan de Fuca, within the Dixon Entrance, and in the Beaufort Sea that conflicted with claims of Canada. no change to map
May 26, 1977 Several parcels were exchanged between Texas and Mexico along the Rio Grande in areas near Presidio and Hidalgo, Texas, including the Horcón Tract, on which the town of Río Rico was located, and Beaver Island near Roma, Texas. In addition, Mexico ceded 823 acres (3.33 km) to the U.S., while the U.S. ceded 2,177 acres (8.81 km) to Mexico, primarily to straighten sections of the Rio Grande for flood control. Map of the change to the United States in central North America on May 26, 1977
December 16, 1977 A treaty defining the maritime border with Cuba was signed; though it has never been ratified by the United States Senate, it is provisionally enforced by agreement renewed every two years. no change to map
October 1, 1978 Tuvalu became independent from the United Kingdom. It claimed the atolls of Funafuti, Nukufetau, Nukulaelae, and Niulakita. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on October 1, 1978
July 12, 1979 The Republic of Kiribati became independent from the United Kingdom. It claimed Birnie Island, Canton Island, Caroline Island, Christmas Island, Enderbury Island, Flint Island, Gardner Island, Hull Island, Malden Island, McKean Island, Phoenix Island, Starbuck Island, Sydney Island, and Vostok Island. This dissolved the condominium of the Canton and Enderbury Islands. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on July 12, 1979
October 1, 1979 The Panama Canal Zone was ceded to Panama. The United States and Panama continued to share operational control of the canal until December 31, 1999, when it would be fully turned over to Panama. The United States retained control over several hundred specified areas to be turned over in piecemeal fashion over the years. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on October 1, 1979
November 24, 1980 The maritime border between the United States and Venezuela was defined. no change to map
September 17, 1981 The United States recognized the sovereignty of Colombia over Roncador Bank and Serrana Bank, and the claim on Quita Sueño Bank was abandoned by the United States, as it was no longer above the seas at high tide, and thus the government considered it unclaimable. Caribbean Sea:
Map of the change to the United States in the Caribbean Sea on September 17, 1981
September 3, 1983 The United States recognized the sovereignty of the New Zealand territory of Tokelau over Atafu, Fakaofo, and Nukunono, and defined the maritime border with Tokelau. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on September 3, 1983
September 8, 1983 The United States recognized the sovereignty of the Cook Islands over Manihiki, Penrhyn, Pukapuka, and Rakahanga, and the maritime border with the Cook Islands was defined. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on September 8, 1983
September 23, 1983 The United States recognized the sovereignty of Kiribati over Birnie Island, Canton Island, Caroline Island, Christmas Island, Enderbury Island, Flint Island, Gardner Island, Hull Island, Malden Island, McKean Island, Phoenix Island, Starbuck Island, Sydney Island, and Vostok Island.

The United States recognized the sovereignty of Tuvalu over Funafuti, Nukufetau, Nukulaelae, and Niulakita.

Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on September 23, 1983
October 12, 1984 The International Court of Justice made its judgment on where the maritime border should be in the Gulf of Maine between the United States and Canada. No land changed hands. The scope of the case did not include the sovereignty of Machias Seal Island, but the judgment enabled defining the extent of the disputed water area around that island (an area of 210 square nautical miles). no change to map
October 21, 1986 The Marshall Islands District of the Trust Territory of the Pacific Islands became independent as the Republic of the Marshall Islands. The Marshall Islanders had claimed Wake Island as part of their territory since at least 1973, and continued that after independence. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on October 21, 1986
November 3, 1986 Most of the Trust Territory of the Pacific Islands was dissolved by the United Nations. The districts of Chuuk, Pohnpei, and Yap became independent as the Federated States of Micronesia. The Mariana Islands District, having already been taking moves towards integration with the United States, became a territory of the United States, the Commonwealth of the Northern Mariana Islands. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on November 3, 1986
June 1, 1990 The maritime border between the United States and the Soviet Union was provisionally defined. The two countries agreed on this date to abide by the terms of the treaty pending its ratification and entry into force, but while it was ratified by the United States Senate on September 16, 1991, it was never ratified by the Soviet Union or its successor state, Russia. no change to map
October 1, 1994 The remaining district of the Trust Territory of the Pacific Islands, the Palau District, became independent as the Republic of Palau, dissolving the TTPI. Pacific Ocean:
Map of the change to the United States in the Pacific Ocean on October 1, 1994
June 1, 1995 The maritime border between the United States and territories of the United Kingdom in the Caribbean Sea was defined. no change to map
January 16, 1997 Navassa Island was transferred to the United States Department of the Interior.
November 13, 1997 The maritime border between the United States and Mexico was defined.
May 26, 1998 The Supreme Court ruled that extra land added to Ellis Island since the original island was officially granted to New York in an interstate compact with New Jersey in 1834 belonged to New Jersey, because the island was within the territorial waters of New Jersey. The original natural boundary of Ellis Island remained an enclave of New York. Map of the change to the United States in central North America on May 26, 1998
December 31, 1999 All former Panama Canal Zone parcels not turned over since 1979, as well as all joint canal operations areas, were transferred to Panama. too small to map
January 17, 2001 The maritime border between the United States and Mexico on the continental shelf in the western Gulf of Mexico beyond 200 nautical miles was defined. no change to map
November 24, 2009 Six islands along the Rio Grande were ceded from Texas to Mexico, and three islands and two bancos were ceded from Mexico to Texas. The transfer, which had been pending for 20 years, was the first application of Article III of the 1970 Boundary Treaty. too small to map
September 23, 2014 The maritime border between the United States and Niue was defined. The treaty was signed on May 13, 1997, but it was not ratified by the United States until at least 2002, and the United Nations shows it as entering into force on this date. no change to map
January 1, 2017 The border between North Carolina and South Carolina was clarified following years of surveys and negotiation, moving 19 homes across state lines. too small to map
November 30, 2020 The State of Rhode Island and Providence Plantations adopted a constitutional amendment, renaming itself the State of Rhode Island. Map of the change to the United States in central North America on November 30, 2020

Bancos along the Rio Grande

An example of a banco, created when a meander is cut off by a new, shorter channel, leaving a cut-off section of land surrounded by a U-shaped (oxbow) lake

The Banco Convention of 1905 between the United States and Mexico allowed, in the event of sudden changes in the course of the Rio Grande (as by flooding), for the border to be altered to follow the new course. The sudden changes often created bancos (land surrounded by bends in the river that became segregated from either country by a cutoff, often due to rapid accretion or avulsion of the alluvial channel), especially in the Lower Rio Grande Valley. When these bancos are created, the International Boundary and Water Commission investigates if land previously belonging to the United States or Mexico is to be considered on the other side of the border. In all cases of these adjustments along the Rio Grande under the 1905 convention, which occurred on 37 different dates from 1910 to 1976, the transferred land was minuscule (ranging from one to 646 acres) and uninhabited.

See also

Notes

  1. The borders of the country followed the colonial borders; for simplicity, the maps use the borders defined in the 1783 Treaty of Paris. The only substantive difference between the borders before and after the Treaty of Paris is the southwest border: when Great Britain had ownership over West Florida, they had moved its border north, to a line east from the mouth of the Yazoo River, and that area thus did not belong to Georgia; the treaty granted the area between this and 31° north to the United States.
  2. The New Hampshire towns petitioning to join Vermont were: Apthorp (now Littleton), Bath, Canaan, Cardigan (now Orange), Cornish, Dresden (now part of Hanover), Enfield, Franconia, Gunthwaite (now Lisbon), Haverhill, Landaff, Lebanon, Lyman, Lyme, Orford, and Piermont. The specific extent of the towns annexed is unknown, as township borders were often delineated only when a dispute arose; the map uses the common interpretation.
  3. The New Hampshire towns petitioning to join Vermont were: Acworth, Alstead, Bath, Cardigan (now Orange), Charlestown, Chesterfield, Claremont, Cornish, Croydon, Dorchester, Dresden, Franconia, "Gilsom" (likely Gilsum), Grafton, Grantham, Gunthwaite (now Lisbon), Hanover, Haverhill, Hinsdale, Landaff, Lancaster, Lebanon, "Leinster" (possibly Lempster), Lincoln, Lyman, Lyme, Marlow, Newport, Piermont, Plainfield, Richmond, Saville (now Sunapee), Surry, Walpole, and Westmoreland. The specific extent of the towns annexed is unknown, as township borders were often delineated only when a dispute arose; the map uses the common interpretation.
  4. The New York towns petitioning to join Vermont were: "Black-Creek" (unknown; possibly is or is near Hebron), Cambridge, Fort Edward, Granville, "Greenfield" (unknown; there is a town named Greenfield but it lies west of the Hudson River, which was explicitly the western extent of the West Union), Hoosick, Kingsbury, "Little Hoosack" (unknown; presumably near Hoosick), Saratoga, "Scorticook" (possibly Schaghticoke), Skeensborough (now Whitehall), and "Upper-White-Creek" (probably White Creek). The specific extent of the towns annexed is unknown, as township borders were often delineated only when a dispute arose; the map uses the common interpretation.
  5. The treaty established the boundaries of the new country, from the Bay of Fundy: up the "St. Croix River" (which river this referred to was disputed) to its source; north to the height of the land (the "Northwest Angle of Nova Scotia"); along the height of the land to the "northwesternmost Head" of the Connecticut River (which source this referred to was disputed); down that to 45° north; west to the St. Lawrence River; up that to the Great Lakes, through Lake Ontario, the Niagara River, Lake Erie, the Detroit River, Lake St. Clair, the St. Clair River, Lake Huron, and Lake Superior; to "Long Lake" (which lake this referred to was disputed) towards the Lake of the Woods; to the northwest angle of the Lake of the Woods; then west to the Mississippi River. However, the Lake of the Woods was north of the source of the Mississippi River; maps universally show this undefined border as a straight line, nearly straight south, between the two points. From there, it followed the Mississippi River down to 31° north; east to the Chattahoochee River; down that to the confluence of the Chattahoochee and Flint rivers; a line from there to the source of the St. Mary's River; then down that to the Atlantic Ocean.
  6. There is disagreement over if the state was named Franklin or Frankland; sources tend to refer to Franklin as the specific state, and Frankland as the region.
  7. Massachusetts's ceded claim was a strip of land west of New York and Pennsylvania stretching to the Mississippi River, bounded by the latitudes of Massachusetts Bay Colony's original charter: on the north by a line west from one league north of Lake Winnipesaukee, and on the south by a line west from Massachusetts' southwest corner.
  8. Connecticut's ceded claim was a strip of land west of 120 miles west of Pennsylvania (the western border of its Western Reserve) stretching to the Mississippi River, bounded by 41° north and the southern edge of Massachusetts's western claim, roughly 42°2′ north.
  9. Massachusetts's ceded claim was the portion of New York 82 miles west of where the Delaware River left New York, to an unclear western boundary, with one source saying it was as far as one mile east of the Niagara River.
  10. The new North Carolina–federal border was, from the north, southwest along various ridges of the Great Smoky Mountains; however, issues caused surveyors to eventually run a line roughly due south rather than continue along the ridge.
  11. The new New York–Vermont border was, from the north: Lake Champlain, the Poultney River, then south following borders of townships.
  12. The new Kentucky–Virginia border was, from the south: north along the Cumberland Mountains and Pine Mountain to the Russell Fork; northeast to the Tug Fork; then down that to the Big Sandy River and to the Ohio River.
  13. The new Indiana Territory–Northwest Territory border was, from the south, a line from the mouth of the Kentucky River to Fort Recovery, then north.
  14. The new Georgia–federal border was, from the south, up the Chattahoochee River to its great bend (near West Point), then a line from there towards and past Nickajack. The border's description said it would go until it reached the Tennessee River, and follow that up the river to Tennessee, but the river lay entirely within Tennessee.
  15. There was some question as to whether the purchase also included the basins of the Missouri River and the Red River of the North, but the question was not relevant before the Treaty of 1818 definitively settled the border. Maps universally show the purchase including the Missouri River basin but excluding the Red River basin.
  16. The western border of West Florida was a series of waterways, mainly the Mississippi, Iberville, and Amite Rivers, and Lakes Pontchartrain and Maurepas.
  17. The new Illinois Territory–Indiana Territory border was, from the south, the Wabash River up to Post Vincennes, then north.
  18. The northwestern remainder of Orleans Territory presumably rejoined Louisiana Territory, as its extent was still vaguely defined.
  19. Indiana was defined as the territory north of the Ohio River and east of the Wabash River, but while the territory's line turned north at Post Vincennes, the state's border continued up the Wabash until it reached the point where a line drawn north from Post Vincennes would last intersect the river as it weaved back and forth. The northern border of the state was a line east from 10 miles north of the southern tip of Lake Michigan, until it reached the meridian that formed Ohio's western border, which was a line drawn north from the mouth of the Great Miami River.
  20. The new Alabama Territory–Mississippi Territory border was, from the north: up the Tennessee River to Bear Creek (around today's Pickwick Lake); a line to the northwestern corner of Washington County, Mississippi Territory; then south.
  21. The new Arkansaw Territory–Missouri Territory border was, from where the Mississippi River meets 36° north: west to the St. Francis River, up that to 36°30′ north, then west.
  22. The new border was, from the Gulf of Mexico: up the Sabine River to 32° north; north to the Red River; up that to 100° west; north to the Arkansas River; up that to its source; north to 42° north; then west to the Pacific Ocean.
  23. The new Missouri–federal border was, from the mouth of the Des Moines River: up the river to a point west of the Des Moines Rapids on the Mississippi River, west to a point north of the mouth of the Kansas River, then south.
  24. The new Arkansas Territory–federal border, from the north, a line from the southwestern corner of Missouri to a point on the Arkansas River "100 paces east" of Fort Smith, as the border of the lands of the Eastern Choctaw, then south. However, the Arkansas Supreme Court determined in 1909 that the "100 paces east" was a clerical error, and that logically it should have said "100 paces west".
  25. The new Michigan Territory–Wisconsin Territory border was, from Lake Superior: up the Montreal River to Lac Vieux Desert; a line to the source of the Menominee River; then down that to Green Bay. However, this definition was impossible: The Montreal River ended long before it reached Lac Vieux Desert. The issue would be resolved in 1850.
  26. The new northeastern border was, from Passamaquoddy Bay: up the St. Croix River to its source; north to the St. John River; up that to the St. Francis River; up that to its source outlet at Lake Pohenegamook; southwest to the northwest branch of the St. John River; a line from there to where the St. John River crosses 46°25’ north; up the river to its source; along the highlands to the source of Halls Stream, then down that to 45° north.
  27. The new northern border was, from Lake Superior: up the Pigeon River to the many lakes and rivers of the Boundary Waters, eventually reaching the Rainy River; then down that to the Lake of the Woods.
  28. The new Wisconsin–Wisconsin Territory border was, from Lake Superior: up the St. Louis River to its first rapids; south to the St. Croix River; then down that to the Mississippi River.
  29. The new international border was, from the Rio Grande: along the southern and western border of New Mexico until it meets the Gila River; down that to the Colorado River; then a line to a point one league south of the port of San Diego. However, the southern border of New Mexico was in question, with the US claim being 31°52′ north, and the Mexican claim being 32°22′ north.
  30. The new California–federal border was, from the north: south along 120° west to 39° north; a line to where the Colorado River intersects 35° north; then down the Colorado River.
  31. The new Texas–federal border was, from the south: up the Rio Grande to 32° north; east to 103° west; north to 36°30′ north; then east.
  32. The new New Mexico Territory–federal border was, from 36°30′ north and 103° west: north to 38° north; then west to the summit of the San Juan Mountains (called then the Sierra Madre).
  33. The new international border was, starting from where the Rio Grande crosses 31°47′ north: west 100 miles; south to 31°20′ north; west to 111° west; a line to a point on the Colorado River 20 miles below the mouth of the Gila River; then up the Colorado River.
  34. The new Minnesota–federal border was, from the north: up the Red River to the Bois de Sioux River; up that to Lake Traverse and its southern tip; a line to Big Stone Lake and through that to its southern tip; then south.
  35. The new Oregon–Washington Territory border was, from the north, up the Snake River to the mouth of the Owyhee River, then south.
  36. The claimed borders of Jefferson Territory were between 37° north, 43° north, 102° west, and 110° west.
  37. The borders of Colorado Territory were parallels 37° north and 41° north, and Washington meridians 25° west and 32° west.
  38. The new Nebraska Territory–Dakota Territory border was, from the east: up the Missouri River to the Niobrara River; up that to the Keya Paha River; up that to 43° north; then west.
  39. The decree transferred land from the left bank of the Blackstone River to Rhode Island, including what is now East Providence, in exchange land around Fall River being transferred to Massachusetts.
  40. The Virginia counties that became West Virginia were: Barbour, Boone, Braxton, Brooke, Cabell, Calhoun, Clay, Doddridge, Fayette, Gilmer, Greenbrier, Hampshire, Hancock, Hardy, Harrison, Jackson, Kanawha, Lewis, Logan, McDowell, Marion, Marshall, Mason, Mercer, Monongalia, Monroe, Morgan, Nicholas, Ohio, Pendleton, Pleasants, Pocahontas, Preston, Putnam, Raleigh, Randolph, Ritchie, Roane, Taylor, Tucker, Tyler, Upshur, Wayne, Webster, Wetzel, Wirt, Wood, and Wyoming.
  41. The new Idaho Territory–Montana Territory border was, from the north: south along 39° west from Washington to the crest of the Bitterroot Range and the Rocky Mountains; then along that to the new tripoint with Dakota Territory.
  42. The new Dakota Territory–Idaho Territory border was, from the south: north along 33° west from Washington to the crest of the Rocky Mountains, then northwest along that to the new tripoint with Montana Territory.
  43. The borders of the Department of Alaska were, from the Dixon Entrance: Up the Portland Channel to 56° north; then along the "summit of the mountains situated parallel to the coast" (the definition of which was disputed) to 141° west; then north.
  44. The borders of Wyoming Territory were parallels 41° north and 45° north, and Washington meridians 27° west and 34° west.
  45. The new Oklahoma Territory–federal border was, from where the Red River meets 98° west: north to the Canadian River; down that to Seminole land; north along that border to the North Canadian River; down that to Creek land; north and east along that border to 96° west; then north. This omits the Cherokee Outlet, whose complex borders separated the main portion of Oklahoma Territory from the former Public Land Strip.

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