All of the Revolutionary-era buildings are destroyed before the evacuation during the Siege of Fort Mifflin in 1777. In the reconstruction of the fort, the Blacksmith Shop is constructed in 1798. The earliest description of it comes from an 1802 inspection report by Major Jonathan Williams (1750 –1815), describing it as "the Blacksmith Shop, a brick building, two fires, twenty feet by nineteen.” It is considered the oldest building on the grounds today.