Hughes County, South Dakota Hughes County, South Dakota Hughes County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 17,022, making it the least populous capital county in the nation, and the twelfth-most populous county in South Dakota. Its county seat is Pierre, the state capital. The county was created in 1873 and organized in 1880. It was named for Alexander Hughes, a legislator. Hughes County is part of the Pierre, SD Micropolitan Statistical Area. According to the U.S. Census Bureau, the county has a total area of , of which is land and
South Dakota Highway 21 was completely concurrent with US 81, which was also established at this time. This concurrency extended from the Nebraska state line to the North Dakota state line. By 1935, all of SD 21 was decommissioned except for its current alignment. South Dakota Highway 21 South Dakota Highway 21 (SD 21) is a state highway in the eastern part of the U.S. state of South Dakota. It connects Lake Norden and Hayti, completely within the south-central part of Hamlin County. SD 21 originally extended from the Nebraska state line to the North Dakota state line, completely concurrent with U.S. Route 81