Stanley County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 2,980. Its county seat is Fort Pierre. The county was created in 1873, and was organized in 1890. It is named for David S. Stanley, a commander at Fort Sully from 1866 to 1874, which was located nearby.

Hughes County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 17,765, making it the least populous capital county in the nation, and the 12th most populous county in South Dakota. Its county seat is Pierre, which is also the state capital. The county was created in 1873, and was organized in 1880. It was named for Alexander Hughes, a legislator. On June 4, 1891, the county's area was increased by the addition of Farm Island, in the Missouri River downstream of Pierre.