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.

Pierre is the capital city of the U.S. state of South Dakota and the County seat of Hughes County. The population was 14,091 at the 2020 census, making it the 2nd least populous US state capital after Montpelier, Vermont. It is South Dakota's 9th most populous city. Pierre is the principal city of the Pierre Micropolitan Statistical Area, which includes all of Hughes and Stanley counties.