Union County is in Southeast South Dakota. Of the 66 counties in the Coyote State, Union County ranks 62nd in terms of size (298,961 acres). South Dakota's Union County has roughly 1,000 acres of undeveloped land for sale based on recent Land Network data. The combined market value of land and rural real estate for sale here was roughly $3 million. The average price of undeveloped acreage for sale in Union County was $489,880. Browse all South Dakota undeveloped land for sale on the Land Network to find your next commercial property or land investment.