The Union County State Fish & Wildlife Area was acquired by the Illinois Department of Natural Resources in the late 1940s and developed a wintering goose population in excess of 50,000 birds by 1964. Since then, controlled harvest through the quota system and continued provision of quality winter sanctuary and food have contributed to a total southern Illinois winter population of nearly 500,000 Canada geese. The Union County segment of this population varies from 50,000 to 100,000 each winter.

The area encompasses 6,202 acres in the Lower Mississippi River bottomlands division of Illinois. Numerous shallow sloughs and other water areas totaling approximately 1,100 acres are scattered throughout the area. More prominent water areas include Grassy Lake with 350 acres and Lyerla Lake with 275 acres. Of the 5,350-acre land area, approximately 2,400 acres are cultivated. The remaining acreage is timber, brush or permanent grass cover. Each year a variety of hard grain and green forage crops are planted and left standing to provide food for the wintering geese. Union County State Fish & Wildlife Area is a haven for many diverse forms of wildlife including white-tailed deer, and bald and golden eagles.

Public use in the refuge is limited. Sightseeing and wildlife photography are permitted and the area is one of the few places in Illinois where so many wild geese can be closely observed and photographed in their natural habitat. Fishing is permitted from March 1 to October 15. Grassy Lake is a shallow, fertile bottomland lake with catfish, the primary sport fish attraction. Excellent early spring and late summer bluegill and crappie fishing exists in Lyerla Lake. Approximately 2,050 acres at the south end of the main site are designated as a Public Hunting Area.