^Southbound trailblazer at Interstate 80 near Mokena, June 2021.
US Route 45 spends a longer distance in the state of Illinois than any other route designation, spanning north-south from the Wisconsin border to the Kentucky border. It runs through Chicago's northwest, western, and southwestern suburbs, thence continuing south through Kankakee, Champaign, Effingham, and southernmost Illinois before crossing the Ohio River into Paducah, Kentucky. Between southwest Chicagoland and Effingham, US Route 45 closely parallels Interstate 57.
US Route 45 enters Illinois crossing the border from Wisconsin, about three miles west of Interstate 94 and eleven miles west of the Lake Michigan shoreline:
US Route 45 crosses Illinois 173 between Zion and Antioch:
Near Lindenhurst, US Route 45 crosses a curving Illinois 132:
US Route 45 meets a 4-way intersection with Illinois 120 on the east side of Grayslake:
In the northwest corner of Libertyville, US Route 45 passes under Illinois 137, but a makeshift fountain interchange provides access:
As US Route 45 makes its way into Mundelein, it crosses Illinois 176:
On the south side of Mundelein, US Route 45 crosses Illinois 60:
Just after crossing Illinois 60, US Route 45 meets another intersection where it ricochets southeastward off of Illinois 83:
Near Lincolnshire, US Route 45 joins Illinois 21 southward:
Right after the union of US Route 45 and Illinois 21, the two routes run concurrently through a junction with Illinois 22:
US Route 45 and Illinois 21 finally split up, with Illinois 21 heading more southeasterly, at a point where Mount Prospect meets Northbrook:
US Route 45 now enters Des Plaines, crossing Illinois 58 on the north side of town:
After another one-third of a mile, US Route 12 comes from the northwest to join US Route 45 south for a long time...
US Routes 45 and 12 cross US Route 14 in downtown Des Plaines...
On their way out of Des Plaines, US Routes 45 and 12 pass under Interstate 90 with no access, but then meet Illinois 72 at an at-grade intersection...
Along the east edge of O'Hare Airport, US Routes 45 and 12 meet a directional interchange with Interstate 190, which can be used to access Interstates 90 or 294 if desired...
Just west of Schiller Park, US Routes 45 and 12 cross Illinois 19 by the southeast corner of O'Hare's expansive property:
At Stone Park, US Routes 45 and 12 pass over Illinois 64, with access provided by a makeshift cloverleaf interchange using Illinois 64's frontage roads...
On the western edge of Melrose Park, US Route 20 comes from the northwest to join US Routes 45 and 12 south...
In Bellwood, US Routes 45, 20, and 12 meet the eastern end of Illinois 56:
As US Routes 45, 20, and 12 enter Westchester, they meet a full interchange with Interstate 290:
After less than half of a mile, US Routes 45, 20, and 12 meet the eastern end of Illinois 38, which once followed Roosevelt Road farther east into the big city:
US Routes 45, 20, and 12 meet a cloverleaf interchange with Interstate 55 near Countryside and Hodgkins:
Between Willow Springs and Justice, US Routes 45, 20, and 12 pass under Interstate 294 with no access, but a fully directional interchange provides full access to Illinois 171:
Near Hickory Hills, US Route 45 finally gets rid of US Routes 20 and 12, which head eastward on 95th Street toward an interchange with Interstate 294:
US Route 45 has a series of exits to access Illinois 83, which passes overhead:
In Orland Park, US Route 45 passes under Illinois 7, but 143rd Street's western approach can provide access...
US Route 45 then crosses US Route 6, still in Orland Park...
A partial cloverleaf interchange provides access to Interstate 80, as US Route 45 enters the Mokena area: