^Northbound trailblazer at 143rd Street near Interstate 355 and the town of Lockport, May 2022.
Illinois 171 runs north-south largely near and to the west of Chicago, in the western and southwestern suburbs. It begins in Joliet, loosely following the east side of the Des Plaines River, northeast to Summit. At Summit, the route turns from a southwest-northeast alignment into a straighter north-south route through Cook County's inner suburbia. Finally, Illinois 171 ends just east of O'Hare, in the northwestern reaches of the Chicago city limits.
From south to north, Illinois 171 starts in Joliet at US Route 6:
From south to north, Illinois 171 starts in Joliet at US Route 6:
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The next route Illinois 171 encounters is Illinois 7 at a 4-way intersection in downtown Lockport.
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Illinois 83 joins from the southeast to cross the Des Plaines River after following loosely alongside it:
Illinois 83 splits apart from Illinois 171 to head north toward Willowbrook:
Illinois 171 has a full interchange with US Route 45 (concurrent with US12 and US20) and passes under Interstate 294...
Illinois 171 makes a turn at Summit onto a more north-south routing, and has a directional interchange with Interstate 55:
After using a short segment of freeway, Illinois 171 returns to surface intersections starting with one at US Route 34...
Illinois 171 crosses Interstate 290 with a diamond interchange:
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By Melrose Park, Illinois 171 has a traffic signal at Illinois 64:
Illinois 171 crosses Illinois 19 at another signalized intersection:
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Illinois 171 has a full interchange with Interstate 90 a block before ending:
Just north of the I-90 interchange, Illinois 171 ends at Illinois 72, where the Chicago city limits border Park Ridge.
