U.S. Route 6 in Illinois

U.S. Route 6 crosses the I-74 Bridge from Bettendorf, Iowa south into Moline, concurrent with Interstate 74. It remains with Interstate 74 for 5 miles (8 km) until the intersection with Interstate 280 south of the Rock River. U.S. 6 then turns east at the Quad Cities International Airport. It intersects Interstate 80 as it leaves the Quad Cities area, and closely parallels I-80 for the rest of its length in Illinois.

From the Quad Cities, U.S. 6 travels east through the city of Geneseo. At Sheffield, U.S. 6 overlaps U.S. Route 34 through to Princeton. After an interchange with Interstate 180, U.S. 6 runs with Illinois Route 89 to Spring Valley. In the LaSalle-Peru area, U.S. 6 intersects with Illinois Route 251, U.S. Route 51 and Interstate 39.

U.S. 6 then runs past Ottawa, intersecting with the concurrent Illinois Routes 23/71 before joining with Illinois 71 for 4 miles (6 km). Further east, U.S. 6 runs through Marseilles and Seneca, where Illinois Route 170 terminates. It then runs through Morris and overlaps Illinois Route 47 for a slight northward jog. At Channahon, U.S. 6 has an interchange with Interstate 55.

U.S. Route 6 at U.S. Route 52 on the southwest side of Joliet.

In the Joliet area, U.S. 6 parallels the Des Plaines River and passes beneath the cantilever bridge carrying Interstate 80 over the Des Plaines River. At this point it is called Railroad Street, but it turns onto McDonough Street with U.S. Route 52 as it crosses the river. It then turns north, overlapping Illinois Route 53 (Chicago Street) and then east with U.S. Route 30 (Cass Street). Two blocks north of leaving U.S. 30, U.S. 6 intersects the southern terminus of Illinois Route 171 and turns east onto Maple Road. In New Lenox it intersects with Interstate 355 and becomes the Southwest Highway.

U.S. 6 turns off the Southwest Highway west of Orland Park and becomes 159th Street, a major east–west arterial through that town and the southern suburbs of Chicago. In Calumet City, U.S. 6 joins with Illinois Route 83 south to the Interstates 80/94 (Kingery Expressway), and then follows the Kingery east into Indiana.

On this routing, U.S. 6 (like nearby U.S. 30) never enters the city limits of Chicago.