Sergeant Duncan Mansfield (February 1778 – ??) was in the United States Marine Corps.
Born at Albany, New York, Mansfield enlisted in the Marine Corps at Philadelphia, Pennsylvania, 11 August 1798 and served until 1805. While serving in schooner Enterprise during the war with Tripoli, Sergeant Mansfield volunteered for the cutting‑out expedition led by Lt. Stephen Decatur, Jr., 16 February 1804. Lieutenant Decatur and his 84‑man crew sailed ketch Intrepid, disguised as an Arab ship, into Tripoli Harbor to destroy the recently captured U.S. frigate Philadelphia and prevent her use against the United States.
USS Mansfield (DD-728) was named for him.