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