Twelve days after the destruction of the fort, James Monroe, the acting Secretary of War, hired Major Pierre L'Enfant to construct new defenses. In November 1814, Monroe questioned L'Enfant actions, asking for less spending. On July 14, 1815, work was halted. Two months later, L'Enfant was replaced by Lieutenant Colonel Walker K. Armistead of the U.S. Army Corps of Engineers. The fort was completed on October 2, 1824, at a total cost of $426,000, excluding armament, which had not yet been installed.
Extensive remodeling was performed in the 1840s and the first guns were mounted in 1846. The masonry fort was occupied by soldiers from the First, Third and Fourth U.S. Artillery during its early history. Except for a few guns at the Washington Arsenal, Fort Washington was the only defense for the nation's capital until the Civil War when a circle of temporary forts was built around the city. Battery Rogers and Fort Foote were the only seacoast forts in the system and armed with large Rodman and Parrott cannons. Fort Washington was garrisoned as the outer defense for the city. Companies of the First and Fourth Artillery as well as numerous state artillery units passed through the post during the war.