Иллинойс штатының 31-ші бағдарламалық жолы

State highway in northeastern Illinois, US

Illinois Route 31 (IL 31) is a 58.41 mile (94 km) north–south state highway in northeastern Illinois, United States. It travels from U. S. Route 34 (US 34) in Oswego north to US 12, near the Wisconsin state line, just south of Richmond. and redirects traffic around downtown Algonquin.

SBI Route 31 traveled from Quincy to Canton along various routes. This was dropped in 1935 and was replaced with US 24. In 1937, it was reapplied along other routes on its modern routing. There have been no changes to the routing since. It traveled concurrently with US 30 from Aurora to Geneva at present day IL 38. In 1934, US 430 was removed north of West Dundee after US 14 was formed.

The intersection of IL 31 and IL 120 is now the most congested intersection in McHenry County. IDOT is currently in Phase 1 of a planned widening of IL 31 from IL 176 in Crystal Lake to IL 120 in McHenry. A bypass of McHenry continues to appear in documents planning for a Metra station at Prairie Grove, that include an interchange with the existing IL 31 alignment and the proposed west McHenry bypass alignment to the north of Gracy Road. The west McHenry bypass was originally planned to travel over undeveloped farm lands from north of IL 31 and Gracy Road to IL 120 and Ringwood Road. The corridor was planned to be protected from development in the mid 1990s, but because of a lack of funding, the corridor was never protected from development and has since been developed.

The Western Algonquin Bypass is not the only limited access bypass on the table as of 2015. A southern Algonquin bypass is being constructed as the Longmeadow Parkway, that will have a grade separation with Route 31.