Major Watersheds of Illinois

This map illustrates general boundaries of major watersheds of Illinois. Shades of blue and green indicate watersheds in the Mississippi River basin. Watersheds with shades of green are located in the Illinois River basin. Shades of yellow and brown indicate watersheds in the Ohio River basin. The Cache River drains to both the Mississippi and Ohio Rivers. Drainage to Lake Michigan is in the Great Lakes basin. Its watershed is shaded pink. A watershed is often considered synonymous with drainage basin, and in this context it is the land area that directly drains to a common stream, river, or lake. Watershed boundaries follow topographic highs. Artificial drainage structures such as canals may convey water across topographic watershed boundaries in some areas shown. Features shown on this map are accurate to the scale at which they were originally developed. Communities are displayed as space allowed. LaMBert Conformal Conic projection based on standard parallels 30° and 45°. This map is available online as a 26" x 38" PDF file (2.1MB)