Human history in the area that became Hill City, and the greater Black Hills in particular, started by at least 7000 BC. The Arikara arrived by 1500 AD, followed by the Cheyenne, Crow, Kiowa and Pawnee. In the 19th century, the Lakota Sioux claimed the land, calling it "Paha Sapa". In 1874, Major General George Armstrong Custer led an expedition into the Black Hills, during which gold was discovered in French Creek, south of Hill City. The discovery of gold opened the Black Hills, and the Hill City area, to mining. Hill City was first settled by miners in 1876, who referred to the area as Hillyo. This was the second American settlement in the Black Hills. Hill City is the oldest city still in existence in Pennington County. A post office was constructed and opened on November 26, 1877. The city almost became a ghost town when miners relocated to the northern Black Hills after the discovery of gold there.