Based on 4,892 research-grade iNaturalist observations in Illinois, Eastern Chipmunk is most often recorded in May; in Illinois it behaves like a summer visitor / breeder. It ranks #4 among mammals recorded in the state in our data.
Tamias striatus
Eastern Chipmunk in Illinois by month
Bars show research-grade observations per month. They mix true seasonality with how often people are outdoors, so treat small numbers with caution.
Also seen in Illinois in May

Eastern Cottontail

Eastern Gray Squirrel

White-tailed Deer

Common Raccoon

Muskrat

Eastern Fox Squirrel

Groundhog

Virginia Opossum
Places to look in Illinois
Cahokia
Botanical GardenMorton Arboretum
Shawnee National Forest
Chicago Botanic Garden
Ladd Arboretum
State ParkStarved Rock State Park
FAQ
When does Eastern Chipmunk appear in Illinois?
Mainly April–October, with the most records in May.
How common is Eastern Chipmunk in Illinois?
It ranks #4 by number of iNaturalist observations among mammals in Illinois (4,892 records in our sample).