Illinois Route 158 is an east–west state road in southwestern Illinois. Its western terminus is at Illinois Route 3 in Columbia and its eastern terminus is at U.S. Route 50, in O'Fallon. This is a distance of .
Illinois 158 will be a proposed 4-laned expressway all throughout its proposed route, however, some interchanges will have ramps and some may have traffic lights. This project has drawn much criticism from local residents of these areas. At least one organization, the Stop 158 group, has formed to block construction of the road and refocus use of taxpayer's dollars on a new Mississippi River bridge south of St. Louis.
The Gateway Connector remains unfunded for construction through 2010.