31st Regiment

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 Infantry Regiment (Philippine Commonwealth Army), a unit of the Philippine Commonwealth 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 Wisconsin Volunteer Infantry Regiment