| State: | IL |
| Type: | IL |
| Maint: | IDOT |
| Route: | 91 |
| Map Custom: | yes |
| Length Mi: | 40.72 |
| Length Round: | 2 |
| Length Ref: | [1] |
| Direction B: | North |
| Direction A: | South |
| Terminus A: | in Peoria |
| Terminus B: | in Kewanee |
| Counties: | Peoria, Stark, Henry |
| Established: | 1941 |
| History: | Signed as IL 30 before 1941[2] |
| Previous Route: | 90 |
| Previous Type: | IL |
| Next Type: | IL |
| Next Route: | 92 |
Illinois Route 91 (IL 91) is a rural state route in central Illinois. It runs from the northwest edge of Peoria at U.S. Highway 150 (US 150) to U.S. Highway 34 and Illinois Route 78 south of Kewanee. Illinois 91 is 40.72miles long.
IL 91 serves the cities of Toulon, Wyoming, Princeville, and Dunlap. It travels concurrently with IL 90 around Princeville.
IL 91 does not travel in a straight line between any two major towns. IL 91's endpoints are generally northwest-to-southeast, but the route consists entirely of north–south and east–west stretches.
The Rock Island Trail State Park follows IL 91 for much of its length. This State Park trail is the former right-of-way of a Peoria branch line of the Chicago, Rock Island and Pacific Railroad.
SBI Route 91 was the current U.S. Route 150 from Knoxville to Peoria. Prior to 1936, Illinois Route 30 mostly followed present-day IL 91 and a part of IL 17 east of Galva. Later, IL 30 was rerouted north of Toulon which entirely followed current IL 91. In March 1941, the state announced that IL 91 was replacing the designation of IL 30 from Kewanee to US 150,[3] and has remained so to this day.[2]