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Frost Dates in Illinois
First and last frost dates across Illinois, computed from 96 NOAA weather stations (1991–2020 climate normals). Your exact date depends on your city and microclimate — use the ZIP lookup on the main tool for a station-specific answer.
Last spring frost
Apr 16
statewide median · range Apr 2–May 1
First fall frost
Oct 22
statewide median · range Oct 7–Nov 5
Growing season
188 days
median · range 160–214
Stations used
96
NOAA 1991–2020 normals
Frost dates by city
Median dates from the nearest NOAA station to each city. The "cautious" date is the 10% spring value — planting after it means only a ~10% chance of a later frost.
| City | Nearest station | Last spring frost | First fall frost | Growing season | Safe transplant |
|---|---|---|---|---|---|
| Chicago | Chicago Midway Ap 3Sw · 12 mi | Apr 10 (cautious: Apr 26) | Nov 1 | 203 days | Apr 24 |
| Springfield | Springfield Abraham Lincoln Ca · 5 mi | Apr 14 (cautious: Apr 29) | Oct 20 | 187 days | Apr 28 |
| Rockford | Rockford Gtr Rockford Ap · 6 mi | Apr 24 (cautious: May 8) | Oct 17 | 174 days | May 8 |
How frost varies across Illinois
Spring frost timing spans about 29 days across the state. Cairo in southern Illinois typically sees its last spring frost around April 2, while Elizabeth in northwestern Illinois doesn't clear frost until about May 1. Within any city, low spots and valleys run colder than the station average; areas near buildings and pavement run warmer.
When to plant in Illinois
As a rule of thumb, cool-season crops (lettuce, peas, spinach) can go in 2–4 weeks before your last spring frost; warm-season transplants (tomatoes, peppers) should wait about 2 weeks after it — around April 30 for the statewide median. Check your city's row above rather than the statewide median: a 29-day statewide spread makes the city-level date the one that matters.
These are climate normals (what's typical), not forecasts. For the current year, watch the 10-day forecast around your planting date.
How this is computed
Statewide medians are the median of the 96 NOAA stations' median frost dates — half the stations run earlier, half later. City rows use the nearest station with 30-year freeze records. Dates are 32°F freeze probabilities from NOAA NCEI 1991–2020 U.S. Climate Normals; nothing is estimated or interpolated.
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Frequently asked questions
When is the last frost date in Illinois?
The statewide median last spring frost is April 16, but it ranges from April 2 to May 1 depending on where in the state you are. Use your city's row in the table above, or the ZIP lookup on the main tool, for a station-specific date.
When can I plant tomatoes outside in Illinois?
Warm-season transplants like tomatoes should wait about two weeks after your last spring frost — around April 30 for the statewide median. Your city may differ by weeks; check the "safe transplant" column in the city table.
How long is the growing season in Illinois?
The median growing season across 96 NOAA stations is 188 days, ranging from 160 to 214 days by location.
Why do frost dates vary so much within Illinois?
Frost timing follows latitude, elevation, and local terrain. Across Illinois, last spring frost dates span about 29 days — from around April 2 near Cairo to May 1 near Elizabeth. Microclimates (low spots, valleys, urban heat) shift dates further at the garden level.
Where does this data come from?
All frost dates are computed from the NOAA National Centers for Environmental Information 1991–2020 U.S. Climate Normals freeze data (public domain), using each station's 32°F freeze probability statistics. No dates are estimated or interpolated.