[1] IL 91 serves the cities of Toulon, Wyoming, Princeville, and Dunlap.

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.