^The first eastbound trailblazer in Illinois, at the Wisconsin border, October 2022.
US Route 12 cuts across northeastern Illinois, descending southeasterly from Wisconsin to cross into Indiana on Chicago's South Side. The route has been estranged from downtown Chicago, being rerouted onto US Route 45 (LaGrange Road) south to 95th Street east. This means that US Route 12's southeastward trajectory is interrupted by a detour straight south and straight east to the Indiana border.
US Route 12 enters Illinois from Wisconsin, changing from a freeway to a surface road....
US Route 12 enters Illinois from Wisconsin, changing from a freeway to a surface road....
At Richmond, US Route 12 continues south, crossing Illinois 173:
Farther south into Richmond, US Route 12 gives birth to Illinois 31, which continues south as US Route 12 turns more easterly:
Illinois 59 joins US Route 12 south in Fox Lake...
Soon after that, US Route 12 and Illinois 59 continue south, meeting the western end of Illinois 134...
At Volo, US Route 12 and Illinois 59 continue south crossing Illinois 120 together:
Shortly after that, US Route 12 has a partial interchange sending Illinois 59 south...
US Route 12 continues on its own as a wide 4-lane highway, and it crosses Illinois 22 at Lake Zurich...
On the north side of Palatine, US Route 12 is joined by Illinois 53, which comes from the north...
After less than a mile, US Route 12 crosses Illinois 68, and Illinois 53 leaves US Route 12 to follow Illinois 68 east instead:
US Route 12 meets a partial interchange with the Illinois 53 freeway, where access is only provided to/from the south:
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At Prospect Heights, US Route 12 cuts southeasterly across the north-south Illinois 83...
On the north side of Des Plaines, US Route 12 dives south past Illinois 58:
Not long after that, US Route 12 joins US Route 45 south for a long time...
US Routes 12 and 45 continue together into downtown Des Plaines as a pair of one-way streets, which cross US Route 14...
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US Routes 12 and 45 continue south under Interstate 90 with no access, and then they cross Illinois 72 near Rosemont...
US Routes 12 and 45 pass by O'Hare Airport, with a nearly-full interchange with Interstate 190, the glorified driveway into O'Hare...
Alongside Schiller Park, US Routes 12 and 45 cross Illinois 19...
US Routes 12 and 45 meet a makeshift cloverleaf interchange with Illinois 64, where Northlake meets Melrose Park...
At Melrose Park, US Route 20 comes from the west to join US Routes 12 and 45 south...
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Between Willow Springs and Justice, US Routes 12, 20, and 45 pass under Interstate 294 with no access, to meet an interchange with Illinois 171:
Two miles to the south, US Routes 12 and 20 split from US Route 45 to follow 95th Street east:
US Routes 12 and 20 continue due east to pass under Interstate 294 again, this time with a full interchange...
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At Oak Lawn, US Routes 12 and 20 cross Illinois 50...
On the South Side of Chicago, US Routes 12 and 20 meet an interchange with Interstate 94...
US Routes 12, 20, and 41 enter the state of Indiana very near the Lake Michigan shoreline, passing under the tolled Interstate 90, with a set of scattered ramps providing full access:
