Based on 19,353 research-grade iNaturalist observations in Illinois, Monarch is most often recorded in August; in Illinois it behaves like a summer visitor / breeder. It ranks #1 among butterflies recorded in the state in our data.
Danaus plexippus
Monarch 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 August
Eastern Tiger Swallowtail
Silver-spotted Skipper
Black Swallowtail
Pearl Crescent
Common Buckeye
Small White
Eastern Tailed-Blue
Hackberry Emperor
Places to look in Illinois
State ParkCahokia
Botanical GardenMorton Arboretum
National ForestShawnee National Forest
Botanical GardenChicago Botanic Garden
Botanical GardenLadd Arboretum
State ParkStarved Rock State Park
FAQ
When does Monarch appear in Illinois?
Mainly July–September, with the most records in August.
How common is Monarch in Illinois?
It ranks #1 by number of iNaturalist observations among butterflies in Illinois (19,353 records in our sample).