Fort Mercer was located in an area called Red Bank in what is now the borough of National Park in Gloucester County, New Jersey.

The fort was named in honor of Brigadier General Hugh Mercer who died earlier that year in fighting at the Battle of Princeton.

[5] On October 22, 1777, in the Battle of Red Bank, an attack by 900 Hessian troops under British Major General William Howe, then occupying Philadelphia, was repelled by Fort Mifflin's defenders with heavy losses on the Hessian side, over 500 casualties including the death of their commander, Colonel Carl Emil Kurt von Donop.

Six British warships under the command of Admiral Francis Reynolds were also involved, two of which ran aground while avoiding the chevaux de frise and were soon destroyed by fire during the battle.

The Patriots retook the site and rebuilt the fort, manning it until 1781, when the fighting moved to Yorktown, Virginia, culminating in an American victory and leading to the cessation of hostilities.