Of 66 counties in the Coyote State, Union County is 62nd in terms of its size (467 square miles). Union County is in Southeast South Dakota. A recent survey of Land Network data records approximately 1,000 acres of lakefront property for sale in South Dakota's Union County, which is valued at a combined $2 million. Browse all waterfront property for sale in Union County on the Land Network to find the marina, lakefront and other recreational property that meets your needs, from waterside land perfect as a retirement investment to existing residential waterfront land and property for hunting, fishing and other outdoor-recreation pursuits! The most common type of land for sale by combined acreage in Union County is residential property.