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Ada County
County
James A. McClure Federal Building and U.S. Courthouse in Boise, Idaho.
Seal
Location within the U.S. state of Idaho
Idaho's location within the U.S.
Coordinates: 43°27′N 116°14′W / 43.45°N 116.24°W / 43.45; -116.24
Country	United States
State	Idaho
Founded	December 22, 1864
Named for	Ada Riggs
Seat	Boise
Largest city	Boise
Area
• Total	1,060 sq mi (2,700 km)
• Land	1,053 sq mi (2,730 km)
• Water	7.9 sq mi (20 km)  0.7%
Population
• Total	494,967
• Estimate	518,907
• Density	470/sq mi (180/km)
Time zone	UTC−7 (Mountain)
• Summer (DST)	UTC−6 (MDT)
Congressional districts	1st, 2nd
Website	www.adaweb.net
County Code: 1A

Ada County is located in the southwestern part of Idaho, United States. As of the 2020 census, the county had a population of 494,967, which by 2022 was estimated to have risen to 518,907. Ada County is by far the state's most populous county; it is home to 26.8% of the state's population. The county seat and largest city is Boise, which is also the state capital. Ada County is included in the Boise metropolitan area. The Ada County Highway District has jurisdiction over all the local county and city streets, except for private roads and state roads. In the interior Pacific Northwest east of the Cascade Range, Ada County ranks second in population, behind Spokane County, Washington.

History

Ada County was created by the Idaho Territory legislature on December 22, 1864, partitioned from Boise County. It is named for Ada Riggs, the daughter of H. C. Riggs, a member of the legislature; he established the county and was a co-founder of Boise. Canyon County, which originally included Payette County and most of Gem County, was partitioned from western Ada County in 1891.

Geography

According to the United States Census Bureau, the county has a total area of 1,060 square miles (2,700 km), of which 1,053 square miles (2,730 km) is land and 7.9 square miles (20 km) (0.7%) is water. The Boise River flows through the northern portion of the county, and the northwest border is bounded by the foothills of the Boise Range mountains; the summits are in adjacent Boise County. The southwestern border of the county is bounded by the Snake River.

Adjacent counties

• Gem County - northwest
• Boise County - northeast
• Elmore County - east
• Owyhee County - south
• Canyon County - west

Major highways

• - Interstate 84
• - Interstate 184
• - US 20
• - US 26
• - US 30
• - SH-16
• - SH-21 - Ponderosa Pine Scenic Byway
• - SH-44
• - SH-55 - Payette River Scenic Byway
• - SH-69

County roads and highways are maintained by the Ada County Highway District.

National protected areas

• Boise National Forest (part)
• Snake River Birds of Prey National Conservation Area (part)

Demographics

2010 census

As of the 2010 census, there were 392,365 people, 148,445 households, and 99,282 families in the county. The population density was 372.8 inhabitants per square mile (143.9/km). There were 159,471 housing units at an average density of 151.5 per square mile (58.5/km). The racial makeup of the county was 90.3% white, 2.4% Asian, 1.1% black or African American, 0.7% American Indian, 0.2% Pacific islander, 2.4% from other races, and 2.8% from two or more races. Those of Hispanic or Latino origin made up 7.1% of the population. In terms of ancestry, 19.4% were German, 15.9% were English, 11.8% were Irish, and 8.6% were American.

Of the 148,445 households, 35.6% had children under the age of 18 living with them, 52.4% were married couples living together, 10.0% had a female householder with no husband present, 33.1% were non-families, and 25.0% of all households were made up of individuals. The average household size was 2.58 and the average family size was 3.11. The median age was 34.8 years.

The median income for a household in the county was $55,835 and the median income for a family was $67,519. Males had a median income of $48,290 versus $34,875 for females. The per capita income for the county was $27,915. About 6.9% of families and 10.2% of the population were below the poverty line, including 11.8% of those under age 18 and 6.8% of those age 65 or over.

2000 census

As of the 2000 census, there were 300,904 people, 113,408 households, and 77,344 families in the county. The population density was 285/sq mi (110/km). There were 118,516 housing units at an average density of 112/sq mi (43/km). The racial makeup of the county was 92.86% White, 0.65% Black or African American, 0.69% Native American, 1.74% Asian, 0.15% Pacific Islander, 1.67% from other races, and 2.24% from two or more races. Hispanic or Latino of any race were 4.48% of the population.

There were 113,408 households, out of which 36.20% had children under the age of 18 living with them, 55.10% were married couples living together, 9.40% had a female householder with no husband present, and 31.80% were non-families. 23.80% of all households were made up of individuals, and 6.07% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 3.11.

The county population contained 27.30% under the age of 18, 10.30% from 18 to 24, 32.50% from 25 to 44, 20.80% from 45 to 64, and 9.10% who were 65 years of age or older. The median age was 33 years. For every 100 females, there were 100.6 males. For every 100 females age 18 and over, there were 98.9 males.

The median income for a household in the county was $46,140, and the median income for a family was $54,416. Males had a median income of $37,867 versus $26,453 for females. The per capita income for the county was $22,519. About 5.40% of families and 7.70% of the population were below the poverty line, including 9.20% of those under age 18 and 5.70% of those age 65 or over.

Government and politics

Ada County has traditionally been rather conservative for an urban county. Like Idaho as a whole, it has long been a Republican Party stronghold. The last victory in a presidential election by a Democrat in Ada County was by Franklin D. Roosevelt in 1936. It rejected Lyndon B. Johnson in 1964 during his 44-state landslide. Barry Goldwater carried it by 13 points, a major reason why Idaho was Johnson's closest state. In 2008 the presidential election in Ada County was more competitive than in previous years; John McCain defeated Barack Obama by six percentage points. Obama became the first Democrat to garner as much as 40 percent of the county's vote since Lyndon B. Johnson. In 2016, Donald Trump won the county by only a plurality due to high third party performance. In 2020, whereas the state of Idaho voted very strongly for Trump, he carried Ada County by a slim majority, only beating Joe Biden by around 3 percentage points. The election was close due to Biden's strength in Boise's downtown urban core, which gave him 59.2% of the vote to Trump's 37.4%. This is the narrowest election in decades for Ada County, and the closest a Democrat has come to carrying the county since 1940. Yet, in 2024, this trend reversed, with Trump once again taking the majority in the county with 53.76% of the vote. This was the best performance for a Republican presidential candidate in Ada county since George W. Bush in 2004.

Democratic gubernatorial nominee Jerry Brady carried the county in his 2002 and 2006 races, despite losing statewide in both contests. Another prominent Democrat, Boise mayor David Bieter, was elected in 2007, 2011 and 2015.

Ada County is split between the first and second congressional districts; it is the only county in the state that is not located entirely within one district. As of 2022, the first district is represented by Russ Fulcher and includes Meridian, Eagle and Kuna, while the second district is represented by Mike Simpson and includes most of Boise proper. Both Fulcher and Simpson are Republicans.

In the Idaho Legislature, Ada County is split among nine districts, the most of any county. Each district elects one state senator and two state representatives. As of 2022, In the state senate, Republicans hold five seats and Democrats hold four. In the state house, Republicans hold ten seats and Democrats hold eight. Generally, Democratic strength is concentrated in Boise itself, while Republican strength is concentrated in the western suburbs. Several of the Boise seats were Democratic pickups in 2006.

Each party held all of their respective legislative seats in the 2008 elections, but Republicans won two competitive county commission races.

County offices

The county government is administered by the Ada County Board of Commissioners, a three-member legislative body. Other elected officials include clerk, treasurer, sheriff, assessor, coroner, and prosecutor.

The Idaho Department of Correction operates the South Boise Prison Complex, a correctional facility located in unincorporated Ada County, south of the Boise Airport and east of Kuna.

Education

Public School districts

School districts include:

• Boise School District
• Kuna Joint School District 3
• Melba Joint School District 136
• West Ada School District (Meridian Joint School District 2)

Residents are in the area (and the taxation zone) for College of Western Idaho.

Communities

Cities

• Boise (county seat and state capital)
• Eagle
• Garden City
• Kuna
• Meridian
• Star

Census-designated places

• Avimor
• Hidden Springs

Unincorporated communities

• Mora
• Pleasant Valley
• Sonna

Population ranking

The population ranking of the following table is based on the 2020 census of Ada County.

† county seat

See also

• List of counties in Idaho
• National Register of Historic Places listings in Ada County, Idaho

References

1. ^ "State & County QuickFacts". United States Census Bureau. Retrieved January 15, 2024.
2. "Annual Estimates of the Resident Population for Counties: April 1, 2020 to July 1, 2022". United States Census Bureau. Retrieved January 15, 2024.
3. "Find a County". National Association of Counties. Archived from the original on May 31, 2011. Retrieved June 7, 2011.
4. "Facts About Idaho". Idaho Department of Commerce. 2011. Archived from the original on September 3, 2011. Retrieved November 10, 2011.
5. "Ada County". Retrieved August 28, 2017.
6. "US Gazetteer files: 2010, 2000, and 1990". US Census Bureau. February 12, 2011. Retrieved April 23, 2011.
7. "Annual Estimates of the Resident Population for Counties: April 1, 2020 to July 1, 2023". United States Census Bureau. Retrieved March 31, 2024.
8. "U.S. Decennial Census". United States Census Bureau. Retrieved June 28, 2014.
9. "Historical Census Browser". University of Virginia Library. Retrieved June 28, 2014.
10. "Population of Counties by Decennial Census: 1900 to 1990". United States Census Bureau. Retrieved June 28, 2014.
11. "Census 2000 PHC-T-4. Ranking Tables for Counties: 1990 and 2000" (PDF). United States Census Bureau. Archived (PDF) from the original on March 27, 2010. Retrieved June 28, 2014.
12. "1964 Presidential General Election Results - Idaho". Retrieved January 2, 2018.
13. "ID 2022 Congressional". Dave's Redistricting. Retrieved August 24, 2023.
14. 2008 - General Election Ada County Archived March 21, 2015, at the Wayback Machine
15. November 5, 2002 General Election Results Archived August 27, 2008, at the Wayback Machine
16. November 7, 2006 General Election Results Archived August 27, 2008, at the Wayback Machine
17. Bieter beats Tibbs in Boise mayor race Archived July 14, 2011, at the Wayback Machine
18. "LIVE Elections Results 2015: Boise City, Ada and Canyon County - Story". Archived from the original on March 4, 2016. Retrieved January 7, 2016.
19. Idaho Legislative District Map Archived November 17, 2011, at the Wayback Machine
20. "Idaho Legislative Districts". Archived from the original on November 10, 2008. Retrieved January 2, 2018.
21. "Baseline 08: Idaho Legislature". Ridenbaugh Press. Retrieved January 2, 2018.
22. "Election shows GOP still has the edge in Ada County". Retrieved January 2, 2018.
23. "Voter Registration Totals as of April 6, 2020". sos.idaho.gov. Retrieved June 5, 2020.
24. Leip, David. "Atlas of US Presidential Elections". uselectionatlas.org. Retrieved January 2, 2018.
25. "Ada County". Adaweb.net. Retrieved January 2, 2018.
26. "Assessor". Adacounty.id.gov. Retrieved January 2, 2018.
27. "Ada County Clerk Auditor Recorder > Home". Adacounty.id.gov. Retrieved March 14, 2019.
28. "Ryan Davidson, Dist. 1". Adacounty.id.gov. Retrieved March 22, 2021.
29. "Rick Visser, Dist. 2". Adacounty.id.gov. Retrieved January 2, 2018.
30. "Kendra Kenyon, Dist. 3". Adacounty.id.gov. Retrieved March 14, 2019.
31. "Coroner". Adacounty.id.gov. Retrieved January 2, 2018.
32. "Ada County Prosecutor". Adacounty.id.gov. Retrieved January 2, 2018.
33. "Ada County Sheriff > Home". Adasheriff.org. Retrieved January 2, 2018.
34. "Treasurer". Adacounty.id.gov. Retrieved March 14, 2019.
35. Information Technology Projects. Idaho Department of Correction. March 2011. Retrieved on June 3, 2011.
36. Locations. Idaho Department of Correction. Retrieved on June 4, 2011.
37. "2020 CENSUS - SCHOOL DISTRICT REFERENCE MAP: Ada County, ID" (PDF). United States Census Bureau. Archived (PDF) from the original on July 21, 2022. Retrieved July 21, 2022. - Text list
38. "College of Western Idaho, pg. 1-77" (PDF). Idaho Legislature. January 26, 2022. Retrieved March 12, 2024. - See the map. Also see area 3 in: "TITLE 33 EDUCATION CHAPTER 21 JUNIOR COLLEGES". Idaho Legislature. Retrieved March 12, 2024.
39. "2020 U.S. Gazetteer Files". United States Census Bureau. Retrieved April 8, 2020.
40. Mora ID Google Maps (accessed January 16, 2019)
41. Pleasant Valley ID Google Maps (accessed January 16, 2019)
42. Sonna ID Google Maps (accessed January 16, 2019)

Further reading

• "Ada County". State website. Archived from the original on November 26, 2005. Retrieved September 20, 2005.

External links

• Official website

v t e Places adjacent to Ada County, Idaho
Gem County Boise County Canyon County Ada County, Idaho Elmore County Owyhee County

v t e Municipalities and communities of Ada County, Idaho, United States
County seat: Boise
Cities	Boise Eagle Garden City Kuna Meridian Star‡
CDPs	Avimor Hidden Springs
Unincorporated community	Owyhee Swan Falls
Footnotes	‡This populated place also has portions in an adjacent county or counties
Idaho portal United States portal

v t e Properties on the National Register of Historic Places in Idaho
	Ada Adams Bannock Bear Lake Benewah Bingham Blaine Boise Bonner Bonneville Boundary Butte Camas Canyon Caribou Cassia Clark Clearwater Custer Elmore Franklin Fremont Gem Gooding Idaho Jefferson Jerome Kootenai Latah Lemhi Lewis Lincoln Madison Minidoka Nez Perce Oneida Owyhee Payette Power Shoshone Teton Twin Falls Valley Washington

v t e State of Idaho
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Regions	Boise metropolitan area Cache Valley Central Idaho Columbia River Plateau Eastern Idaho Great Basin Inland Empire Magic Valley North Central Idaho Idaho Panhandle Palouse Southern Idaho Southwestern Idaho Treasure Valley Wasatch Range Wood River Valley Yellowstone
Larger cities	Boise Nampa Meridian Idaho Falls Pocatello Caldwell Coeur d'Alene Twin Falls Lewiston Post Falls Rexburg Moscow Eagle
Smaller cities	Kuna Ammon Chubbuck Mountain Home Hayden Blackfoot Garden City Jerome Burley
Counties	Ada Adams Bannock Bear Lake Benewah Bingham Blaine Boise Bonner Bonneville Boundary Butte Camas Canyon Caribou Cassia Clark Clearwater Custer Elmore Franklin Fremont Gem Gooding Idaho Jefferson Jerome Kootenai Latah Lemhi Lewis Lincoln Madison Minidoka Nez Perce Oneida Owyhee Payette Power Shoshone Teton Twin Falls Valley Washington
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43°27′N 116°14′W / 43.45°N 116.24°W / 43.45; -116.24

• Idaho counties
• Ada County, Idaho
• 1864 establishments in Idaho Territory
• Boise metropolitan area
• Populated places established in 1864