Illinois Route 31
|Maintained by IDOT|
|Length:||58.41 mi (94.00 km)|
|Existed:||1937 – present|
|South end:||US 34 in Oswego|
| US 30 in Montgomery
I-88 / IL 56 / IL 110 in Aurora
I-90 in Elgin
US 14 in Crystal Lake
|North end:||US 12 in Richmond|
|Counties:||Kendall, Kane, McHenry|
Illinois Route 31 (IL 31) is a north–south state road in northeastern Illinois, United States. It runs from U.S. Highway 34 in Oswego north to U.S. Highway 12, near the Wisconsin border, just south of Richmond. Illinois 31 is 58.41 miles (94.00 km) long.
Route description 
Illinois 31 is called Richmond Road north of Illinois 120 and Front Street south of Illinois 120 in McHenry, Main Street in Algonquin, Western Avenue in Carpentersville, Eighth Street in West Dundee, State Street in Elgin, La Fox Street in South Elgin, Second Street in St. Charles, First Street in Geneva, Batavia Avenue in Batavia, Lincolnway in North Aurora, Lake Street (Southbound) and River Street (Northbound) in Aurora. It is also, along with Illinois 25, signed as part of the Fox River Valley area. Illinois Route 31 between Aurora and Geneva was considered part of the Lincoln Highway transcontinental route.
SBI Route 31 ran from Quincy to Canton along various routes. This was dropped in 1935. In 1937, it was reapplied along other routes on its modern routing. There have been no changes to the routing since.
U.S. Route 430 
U.S. Route 430 was commissioned from 1926 to 1934 in the U.S. state of Illinois, and ran from Aurora to Crystal Lake. It ran with US 30 from Aurora to Geneva at present-day Illinois Route 38. US 430 was dropped in 1934 and replaced in its entirety with IL 31.
There have long existed plans for a four-lane limited access bypass to be constructed west of downtown Algonquin. This would alleviate traffic at what is currently the most congested intersection in McHenry County, and divert through traffic. Widening the existing roadway isn't an option due to the close proximity of the buildings of downtown Algonquin to the road.
The bypass would start on the south at Route 31's intersection with Huntington Drive and would loop west of downtown Algonquin northward to the northern village limits. An interchange with Algonquin Road would also be constructed.
The bypass was even featured on the front cover of IDOT (Illinois Department of Transportation)'s Capital Improvements Plan during the Republican George Ryan years but was completely taken off the project list under Democrat Rod Blagojevich's administration. McHenry County is heavily Republican, and partisan politics may have been involved in the decision. The construction cost continues to go up as time goes by, and is now estimated at around $80 million. Even after U.S. Congressman Donald Manzullo secured millions in federal funding for the project, the State of Illinois has failed to match the funding, further delaying the project. A coalition of elected officials in McHenry County has recently made aggressive pushes to get the State to fund and build the Bypass, including a number of news conferences and a trip to the Illinois State Capitol in Springfield.
Major intersections 
||Oswego||0.0||0.0||US 34 (West Washington Street)|
||Montgomery||2.8||4.5||US 30 – Joliet, Sugar Grove||Interchange|
|North Aurora||8.6||13.8||I-88 / IL 56 west / IL 110 (Ronald Reagan Memorial Tollway) – DeKalb, Chicago||Interchange, southern end of IL 56 concurrency|
|9.4||15.1||IL 56 (West State Street)||Northern end of IL 56 concurrency|
|Geneva||15.4||24.8||IL 38 (State Street / Lincoln Highway)|
|St. Charles||17.4||28.0||IL 64 (Main Street)|
|Elgin||26.4||42.5||US 20 – Rockford, Chicago||Interchange|
|29.7||47.8||I-90 (Jane Addams Memorial Tollway) – Chicago, Wisconsin||Interchange|
|West Dundee||31.9||51.3||IL 72 (Main Street)|
||Algonquin||37.0||59.5||IL 62 east (Algonquin Road)||Western terminus of IL 62|
|Crystal Lake||41.2||66.3||US 14 (Northwest Highway)|
|42.8||68.9||IL 176 (Terra Cotte Avenue)|
|McHenry||49.5||79.7||IL 120 west (Elm Street)||Western end of IL 120 concurrency|
|49.9||80.3||IL 120 east (Elm Street)||Eastern end of IL 120 concurrency|
|Richmond||57.9||93.2||US 12 / CR A16 west (Tryon Grove Road)|
- Carlson, Rich. Illinois State Highways Page: Routes 21 thru 40. Last updated March 15, 2006. Retrieved March 22, 2006.
- Illinois Technology Transfer Center (2007). "T2 GIS Data". Retrieved 2007-11-08.
- Google Inc. Google Maps – Illinois Route 31 (Map). Cartography by Google, Inc. https://maps.google.com/maps?saddr=IL-31+N&daddr=42.0110718,-88.2888328+to:E+Kuhn+Rd&hl=en&ll=42.081917,-88.108978&spn=0.833736,1.783905&sll=42.452357,-88.304683&sspn=0.006475,0.013937&geocode=FR0RfAIdAsa7-g%3BFb8JgQIdwNG8-inB4GKg9gQPiDGYfbsaPJez7A%3BFZy_hwIdb4-8-g&mra=me&mrsp=1,0&sz=17&t=m&z=10&via=1. Retrieved January 2, 2013.