Last spring frost
Apr 18
Frost Dates for Illinois City, IL
First fall frost
Oct 24
Growing season
188 days
Hardiness zone
5b
In an average year around Illinois City, IL, the last spring frost (32°F) is about Apr 18 and the first fall frost is about Oct 24, giving roughly a 188-day growing season. To be safe most years, wait until Apr 5 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | May 11 | Apr 29 | Apr 16 |
| Freeze (32°F) | May 2 | Apr 18 | Apr 5 |
| Hard (28°F) | Apr 25 | Apr 8 | Mar 25 |
| Severe (24°F) | Apr 13 | Mar 30 | Mar 9 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 11 | May 7 | May 3 | May 1 | Apr 29 | Apr 25 | Apr 23 | Apr 20 | Apr 16 |
| 32°F | May 2 | Apr 28 | Apr 24 | Apr 21 | Apr 18 | Apr 15 | Apr 12 | Apr 9 | Apr 5 |
| 28°F | Apr 25 | Apr 19 | Apr 14 | Apr 11 | Apr 8 | Apr 6 | Apr 3 | Apr 1 | Mar 25 |
| 24°F | Apr 13 | Apr 6 | Apr 3 | Apr 1 | Mar 30 | Mar 26 | Mar 21 | Mar 15 | Mar 9 |
| 20°F | Apr 2 | Mar 29 | Mar 25 | Mar 20 | Mar 16 | Mar 13 | Mar 9 | Mar 6 | Mar 2 |
| 16°F | Mar 25 | Mar 18 | Mar 14 | Mar 11 | Mar 8 | Mar 5 | Mar 3 | Feb 28 | Feb 23 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Oct 1 | Oct 15 | Oct 27 |
| Freeze (32°F) | Oct 11 | Oct 24 | Nov 6 |
| Hard (28°F) | Oct 21 | Nov 1 | Nov 15 |
| Severe (24°F) | Oct 30 | Nov 11 | Nov 26 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 1 | Oct 5 | Oct 10 | Oct 13 | Oct 15 | Oct 18 | Oct 20 | Oct 23 | Oct 27 |
| 32°F | Oct 11 | Oct 16 | Oct 19 | Oct 22 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 6 |
| 28°F | Oct 21 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 15 |
| 24°F | Oct 30 | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 21 | Nov 26 |
| 20°F | Nov 6 | Nov 11 | Nov 15 | Nov 18 | Nov 21 | Nov 24 | Nov 27 | Dec 1 | Dec 6 |
| 16°F | Nov 13 | Nov 20 | Nov 23 | Nov 26 | Nov 30 | Dec 2 | Dec 6 | Dec 11 | Dec 17 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Illinois City Dam 16, Il, about 5.2 miles away@if(!empty($station['elevation_ft'])), at 550 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Illinois City, IL?
On average, the last spring frost (32°F) around Illinois City, IL is about Apr 18. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 5.
When is the first frost in the fall?
The first fall frost around Illinois City, IL typically arrives about Oct 24. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around Apr 18 on average, or Apr 5 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 188 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 61259 Planting calendar → Illinois frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026