31st Regiment or 31st Infantry Regiment may refer to:
Infantry regiments
- 31 Combat Engineer Regiment (The Elgins), a unit of the Canadian Army
- 31st Infantry Regiment (Thailand), a unit of the Royal Thai Army
- 31st (Huntingdonshire) Regiment of Foot, a unit of the United Kingdom Army
- 31st Infantry Regiment (United States), a unit of the United States Army
Cavalry regiments
- 31st Mechanized Infantry Regiment "Asturias", a unit of the Spanish Army
- 31st Cavalry Regiment (United States), a unit of the United States Army
Artillery regiments
- 31st Reserve Field Artillery Regiment (Ireland), a unit of the Irish Army
Combat support regiments
- 31 (City of London) Signal Regiment, a unit of the United Kingdom Army
American Civil War regiments
- 31st Illinois Volunteer Infantry Regiment
- 31st Iowa Volunteer Infantry Regiment
- 31st New York Volunteer Infantry Regiment
- 31st Infantry Regiment, United States Colored Troops
- 31st Wisconsin Volunteer Infantry Regiment
See also
- 31st Division (disambiguation)
- 31st Group (disambiguation)
- 31st Brigade (disambiguation)
- 31st Battalion (disambiguation)
- 31st Squadron (disambiguation)
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