[2] The town of Okawville is located close to the Kaskaskia, but about 100 miles downstream from the West Okaw.

The West Okaw is about 32 miles (51 km) in length,[3] as measured from the junction of the arms of Lake Shelbyville.

This figure includes the drainage ditches, which extend the stream about eight miles above the natural channel.

The Wisconsin ice sheet advanced roughly to the Lake Shelbyville Dam, forming a terminal moraine.

The meltwater overtopped the moraine, forming the modern Kaskaskia River, which flowed on through land of older Illinoian Stage.