It runs from Illinois Route 9 near Perdueville to the concurrent U.S.

[1] Illinois 115 is a north–south highway from Perdueville to Buckingham; at Buckingham, it turns east but is still marked north–south.

Illinois 115 is an undivided two-lane surface state route 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.