In the U.S. state of Illinois, Interstate 80 is an Interstate Highway that runs from the Quad Cities east to south of Chicago. It is a main east–west route for traffic coming and going through Illinois, especially for cross-country truckers.
Heading eastbound, after crossing the Mississippi River near Rapids City, Illinois, I-80 runs south for about to a junction with I-74. There is an interchange with I-88 along this leg. At the I-74/I-80 junction, I-80 turns to the east, while I-74 continues to the west and the south. I-80 then roughly parallels US 6 near such cities as Geneseo, Princeton, Peru, LaSalle (near which it intersects I-39), Ottawa, Morris, and Joliet (west of which it has a junction with I-55). The proposed Prairie Parkway limited-access highway will terminate at its south end via an interchange with I-80 at Minooka Road approximately west of I-55. East of Joliet, at New Lenox, I-80 widens to six lanes each way at US 30, and intersects the Veterans Memorial Tollway (I-355), which heads north into the western suburbs of Chicago. I-80 continues east into the south suburbs of Chicago. At Country Club Hills, I-80 meets I-57. In Hazel Crest, I-80 merges into the busy eight-lane Tri-State Tollway, and remains part of the tollway for about until it becomes the Kingery Expressway, a freeway that connects with the Borman Expressway in Indiana. The Illinois Department of Transportation (IDOT) has announced long-term plans to widen I-80 to six lanes as far westward as the Ridge Road exit at Minooka. As of late 2011, widening to US 30 has been completed, with a long-term study ongoing to upgrade the section through Joliet.
Exit numbers correspond to the milepost from where they are located, except for those at miles 155, 156, 158 and 160, which are part of I-294 and use its mileposts instead.