When Is the Last Frost in Illinois?
The average last spring frost in Illinois falls between April 7 and April 26 for most ZIP codes, with a statewide median of April 17. At the average date a later frost is still a coin flip, so tender plants wait for the safer 90% date.
| City | Last frost | 90% safe after | First frost | Growing season |
|---|---|---|---|---|
| Chicago | Apr 10 | Apr 25 | Nov 5 | 208 days |
| Aurora | Apr 19 | May 4 | Oct 23 | 185 days |
| Naperville | Apr 28 | May 14 | Oct 16 | 169 days |
| Joliet | Apr 19 | May 7 | Oct 25 | 188 days |
| Rockford | Apr 24 | May 8 | Oct 17 | 174 days |
| Elgin | Apr 26 | May 12 | Oct 18 | 174 days |
| Springfield | Apr 15 | Apr 30 | Oct 22 | 188 days |
| Peoria | Apr 16 | May 4 | Oct 23 | 189 days |
| Champaign | Apr 15 | Apr 29 | Oct 24 | 190 days |
| Waukegan | Apr 30 | May 14 | Oct 19 | 170 days |
| Bloomington | Apr 21 | May 5 | Oct 20 | 181 days |
| Arlington Heights | Apr 19 | May 3 | Oct 26 | 190 days |
| Decatur | Apr 14 | May 1 | Oct 24 | 192 days |
| Orland Park | Apr 19 | May 5 | Oct 22 | 183 days |
| Moline | Apr 24 | May 9 | Oct 18 | 176 days |
| Belleville | Apr 12 | Apr 28 | Oct 20 | 189 days |
| DeKalb | Apr 24 | May 10 | Oct 18 | 177 days |
| Quincy | Apr 8 | Apr 23 | Oct 30 | 204 days |
| Godfrey | Apr 4 | Apr 19 | Nov 5 | 214 days |
Last and first frost: 50% (median) dates of the last spring and first fall 32 °F night. 90% safe after: only a 10% chance of a later spring frost. First frost dates in January fall in the following winter. Each city uses the NOAA station nearest the ZIP code closest to its center.
Across all 170 Illinois weather stations with frost records, median last frost dates run from April 2 at Mt Carmel, IL to May 2 at Mt Carroll, IL. Elevation, valleys that collect cold air and distance from large water bodies explain most of the spread, so a garden a few miles from a listed city can differ by a week or more. The ZIP code lookup above uses the same NOAA data as the frost date calculator for every US ZIP code.
When Is the First Frost in Illinois?
The average first fall frost in Illinois arrives between October 14 and October 29 for most ZIP codes, with a median of October 21. Tomatoes, peppers, basil and squash are damaged at 32 °F, so harvest or cover them before then.
Fall frost can come early: Chicago has a 10% chance of frost before October 24, Aurora has a 10% chance of frost before October 9 and Naperville has a 10% chance of frost before October 1. Hardy crops such as kale, spinach and cabbage tolerate light frosts and keep producing after the first frost date.
When to Plant Tomatoes in Illinois?
Transplant tomatoes in Illinois 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: Apr 17 – Apr 24 in Chicago, Apr 26 – May 3 in Aurora and May 5 – May 12 in Naperville. Start seeds indoors 6 to 8 weeks before the last frost.
| City | Start seeds indoors | Transplant outdoors | Lowest-risk transplant |
|---|---|---|---|
| Chicago | Feb 13 – Feb 27 | Apr 17 – Apr 24 | after Apr 25 |
| Aurora | Feb 22 – Mar 8 | Apr 26 – May 3 | after May 4 |
| Naperville | Mar 3 – Mar 17 | May 5 – May 12 | after May 14 |
| Joliet | Feb 22 – Mar 8 | Apr 26 – May 3 | after May 7 |
| Rockford | Feb 27 – Mar 13 | May 1 – May 8 | after May 8 |
| Elgin | Mar 1 – Mar 15 | May 3 – May 10 | after May 12 |
| Springfield | Feb 18 – Mar 4 | Apr 22 – Apr 29 | after Apr 30 |
| Peoria | Feb 19 – Mar 5 | Apr 23 – Apr 30 | after May 4 |
| Champaign | Feb 18 – Mar 4 | Apr 22 – Apr 29 | after Apr 29 |
| Waukegan | Mar 5 – Mar 19 | May 7 – May 14 | after May 14 |
| Bloomington | Feb 24 – Mar 10 | Apr 28 – May 5 | after May 5 |
| Arlington Heights | Feb 22 – Mar 8 | Apr 26 – May 3 | after May 3 |
| Decatur | Feb 17 – Mar 3 | Apr 21 – Apr 28 | after May 1 |
| Orland Park | Feb 22 – Mar 8 | Apr 26 – May 3 | after May 5 |
| Moline | Feb 27 – Mar 13 | May 1 – May 8 | after May 9 |
| Belleville | Feb 15 – Mar 1 | Apr 19 – Apr 26 | after Apr 28 |
| DeKalb | Feb 27 – Mar 13 | May 1 – May 8 | after May 10 |
| Quincy | Feb 11 – Feb 25 | Apr 15 – Apr 22 | after Apr 23 |
| Godfrey | Feb 7 – Feb 21 | Apr 11 – Apr 18 | after Apr 19 |
Indoors: 6–8 weeks before the average last frost. Outdoors: 1–2 weeks after it. Lowest-risk: after the date with only a 10% chance of a later frost. Rules of thumb; check the 10-day forecast and wait for soil near 60 °F.
Tomatoes stall below about 50 °F at night and are killed by frost, so a week or two of waiting after the average date costs little. The tomato plant care guide covers light, watering and feeding once plants are in the ground.
What Can You Plant in Chicago and When?
Chicago's average last frost of April 10 anchors its spring planting calendar: peas and spinach go in from February 27, broccoli and lettuce transplants from March 13, and tomatoes, peppers and squash after April 17.
| Crop | Start seeds indoors | Plant outdoors | Frost tolerance |
|---|---|---|---|
| Peas | — | Feb 27 – Mar 13direct sow, 4–6 weeks before last frost | hardy |
| Spinach | — | Feb 27 – Mar 20direct sow, 3–6 weeks before last frost | hardy |
| Radishes | — | Mar 6 – Mar 20direct sow, 3–5 weeks before last frost | hardy |
| Onions (sets) | — | Mar 13 – Mar 27plant, 2–4 weeks before last frost | hardy |
| Potatoes | — | Mar 13 – Mar 27plant, 2–4 weeks before last frost | half-hardy |
| Broccoli & cabbage | Feb 13 – Feb 27 | Mar 13 – Mar 27transplant, 2–4 weeks before last frost | hardy |
| Lettuce | Feb 27 – Mar 13 | Mar 13 – Mar 27transplant, 2–4 weeks before last frost | hardy |
| Beets | — | Mar 13 – Mar 27direct sow, 2–4 weeks before last frost | half-hardy |
| Carrots | — | Mar 20 – Mar 27direct sow, 2–3 weeks before last frost | half-hardy |
| Tomatoes | Feb 13 – Feb 27 | Apr 17 – Apr 24transplant, 1–2 weeks after last frost | tender |
| Basil | Feb 13 – Feb 27 | Apr 17 – May 1transplant, 1–3 weeks after last frost | tender |
| Peppers | Jan 30 – Feb 13 | Apr 24 – May 1transplant, 2–3 weeks after last frost | tender |
| Eggplant | Jan 30 – Feb 13 | Apr 24 – May 1transplant, 2–3 weeks after last frost | tender |
| Green beans | — | Apr 17 – May 1direct sow, 1–3 weeks after last frost | tender |
| Sweet corn | — | Apr 17 – May 1direct sow, 1–3 weeks after last frost | tender |
| Cucumbers | Mar 13 – Mar 20 | Apr 17 – May 1transplant, 1–3 weeks after last frost | tender |
| Squash & zucchini | Mar 13 – Mar 20 | Apr 17 – May 1transplant, 1–3 weeks after last frost | tender |
| Watermelon | Mar 13 – Mar 20 | Apr 24 – May 1transplant, 2–3 weeks after last frost | tender |
Dates for Chicago (last frost Apr 10, NOAA station Chicago Northerly Is, IL, 3 miles from ZIP 60608). General rules of thumb; wait for soil near 50 °F for most seeds and 60 °F for beans, corn and squash.
How Long Is the Growing Season in Illinois?
The frost-free growing season in Illinois lasts about 170 to 203 days for most ZIP codes, with a median of 187 days. Among the listed cities, Naperville has the shortest season at 169 days and Godfrey the longest at 214.
Season length decides which varieties ripen: compare it with the “days to maturity” on seed packets, counted from transplanting for tomatoes and peppers. NOAA stations in Illinois range from 154 days at Mt Carroll, IL to 216 days at Grand Chain Dam 53, IL. Planning beds before the season starts helps in short seasons — a plant spacing calculator for vegetable beds shows how many transplants fit.
What Hardiness Zones Are in Illinois?
Illinois spans USDA hardiness zones 5a to 7a, with zone 6a the most common. Zones describe winter cold and decide which perennials survive, while frost dates set when to plant annual vegetables and flowers.
The Illinois planting zone map with the zone of each city shows how the zones are spread across the state and which plants are hardy in all of them.
Frequently Asked Questions
- When is the last frost in Illinois?
- The average last spring frost in Illinois falls between April 7 and April 26 for most ZIP codes, with a statewide median of April 17. Among major cities it ranges from April 4 in Godfrey to April 30 in Waukegan.
- When is the last frost in Chicago, Illinois?
- Chicago's average last spring frost is April 10, and by April 25 the chance of a later frost drops to 10%. Its first fall frost averages November 5, giving a 208-day growing season (NOAA station Chicago Northerly Is, IL).
- When should you plant tomatoes in Illinois?
- Transplant tomatoes in Illinois 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: Apr 17 – Apr 24 in Chicago, Apr 26 – May 3 in Aurora and May 5 – May 12 in Naperville. Start seeds indoors 6 to 8 weeks before the last frost.
- When is the first frost in Illinois?
- The average first fall frost in Illinois arrives between October 14 and October 29 for most ZIP codes, with a median of October 21. Harvest tender crops such as tomatoes, peppers and basil before then or cover them on cold nights.
- How long is the growing season in Illinois?
- The frost-free growing season in Illinois lasts about 170 to 203 days for most ZIP codes, with a median of 187 days, from 169 days in Naperville to 214 days in Godfrey.
Frost data: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals (32 °F freeze dates by probability). ZIP code and city locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. Planting windows are general rules of thumb. PlantoScan is not affiliated with or endorsed by these agencies.