Hanson County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 3,461. Its county seat is Alexandria. The county was founded in 1871 and organized in 1873. It was named for Joseph R. Hanson, clerk of the first legislature. Hanson County is part of the Mitchell, SD Micropolitan Statistical Area. The county is somewhat unique among those in the United States in that there are no officially registered airports within the county borders.