Illinois Route 131
|Green Bay Road|
|Maintained by IDOT|
|Length:||15.15 mi (24.38 km)|
|Existed:||1938 – present|
|South end:||IL 176 in Lake Bluff|
|North end:||WIS 31 in Winthrop Harbor|
Illinois Route 131 is a north–south state road in northeastern Illinois. It extends south from Wisconsin Highway 31 and Lake CR A1/19 (128th Street) at the Illinois/Wisconsin state line by Pleasant Prairie, south to Illinois Route 176 in Lake Bluff, a distance of 15.15 miles (24.38 km).
Illinois 131 is called Green Bay Road for its entire length, but Green Bay Road becomes a residential street and extends south through various North Shore communities to Evanston, a distance of approximately 20 miles (32 km) south of Illinois 176. It is one of very few state routes whose named road is longer than the marked state road. Green Bay Road actually continues south to Old Elm Road (Lake CR 52) while there is a second segment of Green Bay Road that starts at a dead end in Highwood and ends at Ridge Avenue in Evanston.
The road parallels U.S. Route 41 (Skokie Highway), which is only a few miles to the west, and Illinois Route 137 (Amstutz Expressway), which is only a few miles to the east. It is the major north–south road between those two expressways.
SBI Route 131 ran from Mattoon to Greenup in southeastern Illinois. This was dropped in 1937 for Illinois Route 121. The next year, Illinois 131 was used on a road that extended Highway 31 south into Illinois. This had formerly been Illinois Route 68. Had Illinois 31 not already been in use, the road south of Wisconsin may have been designated Illinois 31 instead.