Union County is in Southeast South Dakota. Of the 66 counties in the Mount Rushmore State, Union County ranks 62nd in terms of size (298,961 acres). The total value of 1,000 acres of residential land and property recently listed for sale in South Dakota's Union County was about $16 million. The average price of residential land for sale in Union County was $443,897. Browse all residential land and rural property for sale in South Dakota to find residential land and properties that suit your lifestyle needs, from existing residential homes and estates to land ready for future residential-property development.