The total value of farms and rural land for sale in Illinois's Williamson County recently on Land.com was nearly $28 million. This represents approximately 2,000 acres of farms, rural land, hunting land and other land for sale in Williamson County. Williamson County ranks 29th out of 102 counties in the Land of Lincoln for the combined amount of land currently advertised for sale. Of all locations in Williamson County with land for sale, Marion had the most land for sale. From an economic perspective, government and state-level services contribute most to Williamson County's overall GDP. Williamson County is the 65th largest county (444 square miles) in Illinois. It's located in the Southern Illinois region of Illinois.