Illinois State Highway System
| State Highway System | |
|---|---|
Highway markers for Interstate 57, U.S. Route 45, Illinois Route 1 and the Chicago Skyway | |
| System information | |
| Maintained by IDOT, ISTHA, and SCC | |
| Formed | November 5, 1918 |
| Highway names | |
| Interstates | Interstate X (I-X) |
| US Highways | U.S. Route X (US X) |
| State | Illinois Route X (IL X) |
| System links | |
The organized State Highway System of the U.S. state of Illinois comprises all of the state routes in the state.