The Apalachicola Arsenal, originally known as the Mt. Vernon Arsenal, was built by the United States Army as an arms depot during the Second Seminole Indian War, with construction beginning in 1832 and ending in 1839. The original compound had nine buildings in a 400 ft. by 400 ft. quadrangle behind a 12-foot-high, 30-inch-thick perimeter wall, plus outbuildings. The U.S. Army maintained it until 1861, when Confederate troops took it over. After the Civil War, it was used by the Freedman's Bureau until 1868 and then as the state's first penitentiary. In 1876, it became Florida's first mental health hospital. One original outbuilding, built as a gunpowder storage building or powder magazine, is the only surviving outbuilding from the arsenal. It originally had a hip roof, a single doorway in the south wall, and a high brick containment wall around it. Over time, the Florida State Hospital used the structure as a coffin factory, carpenter shop, sewing center, and mattress factory. After many alterations and a period of neglect and abandonment, its restoration was completed in 2013.