Union County is in Southeast South Dakota. Of the 66 counties in the Coyote State, Union County is 62nd in terms of its size (467 square miles). South Dakota's Union County has almost 1,000 acres of residential land and property for sale based on recent Land Network data. The combined market value of land for sale here was around $26 million. The average price of residential acreage for sale in Union County was $985,217. 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.