Of 102 counties in the state, Union County is 71st in terms of its size (422 square miles). Union County is in Southern Illinois. Union County, Illinois, includes 1,000 acres of lakefront homes and property for sale based on recent Land Network data. The combined market value of farms, hunting land and other rural land and acreage for sale here was $100,000. 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 house.