The Kankakee Arch is a geologic arch with a northwest–southeast trending axis which connects the Cincinnati Arch to the southeast with the to the northwest. It lies beneath northeastern Illinois, northern Indiana and southeastern Wisconsin. This structural ridge lies between the Illinois Basin to the southwest and the Michigan Basin to the northeast. The area of central Illinois began to depress by the late Ordovician. The Cincinnati Arch was developing across eastern Indiana during the late Ordovician. By the Early Silurian the seas northwest of the Cincinnati Arch began to become shallower. By the Early Mississippian, the Kankakee arch was above sea level.