During the American War for Independence, Fort Frederick was revitalized for military use when the Continental Congress turned it into a prison camp for captured British soldiers, making it extremely overcrowded and prone to frequent escape attempts under local militia guard. After the war, Maryland sold the fort and 99.5 acres at public auction in the 1790's. Throughout most of the 19th Century, Nathan Williams, an African American who purchased the property in 1860, farmed Fort Frederick with his family, acquired additional land, built several dwellings and a barn in the northwest bastion, and during the family's 5 years of occupation one of Washington County's first schools for African Americans was established on the property. The fort and surrounding grounds continued in agricultural use until the outbreak of the Civil War in 1861, when the barracks had disappeared and the fort had become little more than a large stonewall. During the winter of 1861-62, a company of Union soldiers from the 1st Maryland Regiment garrisoned the fort, and on Christmas Day, 1861, skirmished with Confederate raiders who had crossed the Potomac River. After the main theater of action shifted elsewhere in 1862, the fort was abandoned again, ending its military use. By the late 19th Century, public interest in preserving Fort Frederick for its historic value had grown, and it became a popular site for patriotic celebrations. In 1922, Maryland acquired the fort and 189.5 acres, and during the 1930s the Civilian Conservation Corps established a camp there, carried out archeological excavations, reconstructed the fort walls, and capped the original building foundations at ground level, helping preserve the fort and develop the site as a State Park.
