81st Regiment
81st Regiment may refer to:
- 81st Regiment of Foot (Aberdeenshire Highland Regiment), a unit of the British Army, 1777–1783
- 81st Regiment of Foot (Loyal Lincoln Volunteers), a unit of the British Army
- 81st Infantry Regiment (Philippine Commonwealth Army), a unit of the Philippine Commonwealth Army during the Second World War from 1942 to 1946.
- 81st Infantry Regiment (Imperial Japanese Army), a unit of the Japanese Army
- 81st Assault Aviation Regiment, later Fighter-Bomber regiment, an aviation unit of the Yugoslav Air Force
- American Civil War
- 81st Illinois Volunteer Infantry Regiment, a unit of the Union (Northern) Army
- 81st Indiana Infantry Regiment, a unit of the Union (Northern) Army
- 81st New York Volunteer Infantry, a unit of the Union (Northern) Army
- 81st Ohio Infantry, a unit of the Union (Northern) Army
- 81st Pennsylvania Infantry, a unit of the Union (Northern) Army