[1] 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.

On its way out of town, it passes the historic Joliet Correctional Center, used as a location in several television shows and movies including The Blues Brothers.

[4][5] The two routes split again immediately north of the bridge, as IL 83 continues north while IL 171 resumes its northeastward course, passing St. James at Sag Bridge Church and Cemetery, listed on the National Register of Historic Places.

Leaving the forest preserve, it passes through the village of Willow Springs which was built strung out along the road.

IL 171 has a complex interchange with US 12/US 20/US 45 (LaGrange Road) and I-294 (Tri-State Tollway) on the border between Willow Springs and Justice.

At an intersection with West 55th Street in Summit, IL 171 bends sharply to the north, becoming a freeway for about two miles (3.2 km), crossing the Illinois and Michigan Canal, the Chicago Sanitary and Ship Canal, the Stevenson Expressway (I-55), and the Des Plaines River at a cloverleaf interchange whose ramps had to be built as bridges over these watercourses due to their close proximity to I-55.

Continuing north into Maywood, it passes Loyola University Medical Center before intersecting I-290 (Eisenhower Expressway).

It then has a cloverleaf interchange with I-90 (Kennedy Expressway) before ending at IL 72 (Higgins Road), at the border between Chicago and Park Ridge, near O'Hare Airport.

[9] This original trail continued northeast beyond Summit around the southern shore of historic Mud Lake as a dry land route past the marshy Chicago Portage, ending where Downtown Chicago is now.

In 1926, a new alignment for the Saint Louis to Chicago through highway was opened as IL 4 on the northwest side of the Des Plaines River from Joliet to Lyons.

This left IL 4A from Joliet to Chicago as an odd remote orphan of its Downstate parent route until it was eliminated in 1967.

[2] In the mid-1960s, as part of the construction of the new Stevenson Expressway, IL 171 was upgraded to a freeway between Summit and Lyons, including its interchange with I-55.

[19] The section of IL 171 on Archer Avenue between Sag Bridge and Justice is reputed to be haunted.