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. Construction began in 1832 and was completed in 1839. The original compound consisted of nine buildings in a 400 ft. by 400 ft. quadrangle behind a 12-foot-high, 30-inch-thick perimeter wall, plus other outbuildings. The U.S. Army maintained the arsenal until 1861, when Confederate troops took it over. Following the Civil War, the arsenal 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. This structure incorporates three of the arsenal's original buildings—an office, guard room, and officer's quarters—and later served as the hospital administrator's residence. The building features a two-story gallery ornamented by decorative brackets, and although portions of the gallery have been enclosed, it retains much of its imposing historic appearance, with segments of the original perimeter wall visible at both ends.