Union County is in Southern Illinois. Of the 102 counties in the Inland Empire, Union County ranks 71st in terms of size (422 square miles). Union County, Illinois, includes nearly 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 roughly $8 million. The average price of residential land for sale in Union County was $515,868. Browse all residential land and rural property for sale in Illinois 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.