Illinois climate almanac
Illinois's climate, read through its 70 NOAA stations, is mainly mild humid continental (northeast, midwest, pacific northwest), then cold continental (upper midwest, rocky mountains). The mean frost-free season runs from about April 19 to October 20, roughly 184 days.
Stations 70 NOAA 1991-2020 normals
Mean frost-free season 184 days 154 to 211 across the state
Typical frost window April 19 - October 20 Median last and first frost
Main climate types 2 Mild humid continental (Northeast, Midwest, Pacific Northwest) (67); Cold continental (Upper Midwest, Rocky Mountains) (3)
What this means for your home
In Illinois, the difference between the shortest and longest frost-free pockets is 57 days. That is the difference between a tomato crop that struggles and one that runs into October, between one fertilizer timing and another. Set your place above to tune every date to your nearest station.
Major cities in Illinois
Pick a city to see its frost and planting dates, or set your own place above.