This response was provided by Darryl Coates, Illinois Department of Natural Resources District Wildlife Biologist.
Hello Randy, Thank you for your observations. I have no doubt in my mind that you are seeing a chipmunk. The Eastern Chipmunk has a wide distribution across the eastern half of the U.S. which includes all counties in Illinois. Chipmunks are usually found in deciduous forest, brushy areas. They are commonly seen in park, recreational areas and camp grounds where grasses are mowed and oak/hickory trees and shrubs are abundant. Other similar species are the Least Chipmunks which is smaller but still have the white facial stripes; however, the stripes on his sides go all the way to the base of the tail and the Thirteen-Lined Ground Squirrel which has broken stripes on sides and back which are more yellowish in color. Now that you know where to look . . . you may find them in new locations.