91st Regiment

91st Regiment or 91st Infantry Regiment may refer to:


 * 91st Regiment of Foot (disambiguation), several units of the British Army
 * 91st Punjabis (Light Infantry), a unit of the British Indian Army
 * 91st Cavalry Regiment, United States
 * 91st Coast Artillery (United States)

Union Army (American Civil War):
 * 91st Illinois Volunteer Infantry Regiment
 * 91st Indiana Infantry Regiment
 * 91st New York Volunteer Infantry Regiment
 * 91st Ohio Infantry
 * 91st Pennsylvania Infantry