Illinois Route 115 is a minor north–south road in northeastern Illinois. It runs from Illinois Route 9 near Perdueville to the concurrent U.S. Routes 45/52 in Kankakee. This is a distance of 63.37 miles (101.98 km).

Illinois 115 is a north–south highway from Perdueville to Buckingham; at Buckingham, it turns east but is still marked north–south. South of Kankakee, Illinois 115 turns north again on its way into Kankakee.

Illinois 115 is an undivided two-lane surface road for its entire length.

SBI Route 115 ran from near Kankakee to Perdueville along what is Illinois 115 now. In 1954, when U.S. 45 was moved onto a new road, Illinois 115 was extended north into Kankakee onto old U.S. 45.