There was a combined around $8 million of farms and ranches for sale in Clay County recently on Land.com. The total acreage of all Clay County farms and ranches for sale was nearly 1,000 acres. Clay County ranks 16th out of 66 counties in the Mount Rushmore State for the combined amount of land currently advertised for sale. Among cities in Clay County with farms, ranches, hunting land and other land for sale, Vermillion had the most land for sale. Government and state-level services are the main economic drivers in Clay County. Clay County is the 66th biggest county (417 square miles) in South Dakota. It's located in the Southeast South Dakota region of the state.