Although to many casual observers Illinois appears to be a monotonous landscape of agricultural fields and urban areas, the state has considerable biological and geological diversity.
Divisions contain different sections sharing common geological and ecological features.
Sections contain a variety of natural communties, each with distinctive biota. Midewin is located in the Grand Prairie Division, the largest of the natural divisions. The topography and soils of the Grand Prairie are the result of its geological history. The fine-textured soils with high clay content are poorly drained in many places, resulting in extensive wet prairies and marshes. Trees are present along streams and in scattered groves, savanna, and upland forest on moraines and other glacial hills.