Fort Mercer was one of two forts constructed in 1777, on the Delaware River during the American Revolutionary War, by the Continental Army. Built by polish engineer Thaddeus Kosciuszko under the command of George Washington, its purpose was to block the approach to Philadelphia, Pennsylvania: Fort Mifflin, on the Pennsylvania side, and Fort Mercer, on the New Jersey side. Fort Mercer was located in what is now the borough of National Park, Gloucester County, New Jersey, United States. A park, monument, and museum exist today on the site of the fort. The fort was named in honor of Brigadier General Hugh Mercer who had died earlier that year at the Battle of Princeton.
On October 22 of that year, in what is known as the Battle of Red Bank, an attack by 900 Hessian troops, serving under British Major General William Howe, who then occupied Philadelphia, was repelled, with heavy losses on the Hessian side, including the death of their commander, Colonel Carl Emil Kurt von Donop, by the 600 Continental defenders under Colonel Christopher Greene. After the later loss of Fort Mifflin, Fort Mercer was abandoned without a fight when Lord Charles Cornwallis landed 2,000 British troops nearby on November 18, 1777.