42nd Regiment or Forty-second Regiment may refer to:
Confederate States 42nd Arkansas Cavalry Regiment 42nd Mississippi Infantry Regiment 42nd Virginia Infantry Regiment
United Kingdom 42nd Deoli Regiment, an infantry regiment of the British Indian Army 42 Engineer Regiment (Geographic), a unit of the British Army Royal Engineers 42nd Regiment of Foot, a unit of the British Army up to 1881, known as the "Black Watch" 42nd Royal Tank Regiment, a World War II armoured unit of the British Army
United States 42nd Illinois Volunteer Infantry Regiment 42nd Indiana Infantry Regiment 42nd Infantry Regiment (United States), a unit of the US Army 42nd Kentucky Infantry Regiment 42nd New York Volunteer Infantry Regiment 42nd Ohio Infantry Regiment 42nd United States Colored Infantry Regiment 42nd Wisconsin Volunteer Infantry Regiment
Other nations 42nd Armoured Regiment (India), a unit of the Union of the Indian Army 42nd Bomber Aviation Regiment, an aviation unit of the Yugoslav Air Force 42nd Field Artillery Regiment (Lanark and Renfrew Scottish), RCA, a unit of the Canadian Army 42nd Infantry Regiment (France), a former unit in the French Army 42nd Infantry Regiment (Poland), a unit of the Polish Armed Forces of the Second Polish Republic
See also 42nd Battalion (disambiguation) 42nd Brigade (disambiguation) 42nd Division (disambiguation) 42nd Group (disambiguation) 42 Squadron (disambiguation)