Illinois Route 171 (IL 171) is a 38.61-mile-long (62.14 km) north–south state highway in northeastern Illinois. It runs from U.S. Route 6 (US 6) in Joliet north to Illinois Route 72 at the Chicago–Park Ridge border. The section of IL 171 on Archer Avenue from Joliet to Summit is historically significant, originating as a Native American trail, and later serving for a time as part of the first numbered highway between St. Louis and Chicago.

U.S. Route 6 (US 6) in the state of Illinois is an east–west arterial surface road that runs 179.88 miles (289.49 km) from the city of Moline in the Quad Cities area to Lansing at the Indiana state line.