Last spring frost
Apr 12
Frost Dates for St. Jacob, IL
First fall frost
Oct 20
Growing season
189 days
Hardiness zone
7a
In an average year around St. Jacob, IL, the last spring frost (32°F) is about Apr 12 and the first fall frost is about Oct 20, giving roughly a 189-day growing season. To be safe most years, wait until Mar 28 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 8 | Apr 23 | Apr 10 |
| Freeze (32°F) | Apr 28 | Apr 12 | Mar 28 |
| Hard (28°F) | Apr 16 | Mar 31 | Mar 14 |
| Severe (24°F) | Apr 6 | Mar 21 | Mar 2 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 8 | May 3 | Apr 30 | Apr 26 | Apr 23 | Apr 20 | Apr 17 | Apr 14 | Apr 10 |
| 32°F | Apr 28 | Apr 22 | Apr 19 | Apr 15 | Apr 12 | Apr 8 | Apr 5 | Apr 2 | Mar 28 |
| 28°F | Apr 16 | Apr 10 | Apr 6 | Apr 3 | Mar 31 | Mar 29 | Mar 25 | Mar 20 | Mar 14 |
| 24°F | Apr 6 | Apr 1 | Mar 29 | Mar 25 | Mar 21 | Mar 17 | Mar 14 | Mar 8 | Mar 2 |
| 20°F | Mar 27 | Mar 21 | Mar 17 | Mar 13 | Mar 9 | Mar 5 | Mar 2 | Feb 26 | Feb 19 |
| 16°F | Mar 18 | Mar 12 | Mar 7 | Mar 3 | Feb 28 | Feb 24 | Feb 18 | Feb 11 | Feb 3 |
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) | Sep 27 | Oct 9 | Oct 23 |
| Freeze (32°F) | Oct 3 | Oct 20 | Nov 1 |
| Hard (28°F) | Oct 15 | Oct 30 | Nov 15 |
| Severe (24°F) | Oct 29 | Nov 10 | Dec 1 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 27 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 19 | Oct 23 |
| 32°F | Oct 3 | Oct 10 | Oct 14 | Oct 17 | Oct 20 | Oct 22 | Oct 25 | Oct 28 | Nov 1 |
| 28°F | Oct 15 | Oct 21 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 4 | Nov 8 | Nov 15 |
| 24°F | Oct 29 | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 13 | Nov 18 | Nov 24 | Dec 1 |
| 20°F | Nov 5 | Nov 10 | Nov 14 | Nov 18 | Nov 22 | Nov 27 | Dec 1 | Dec 5 | Dec 13 |
| 16°F | Nov 15 | Nov 21 | Nov 27 | Dec 1 | Dec 4 | Dec 8 | Dec 14 | Dec 20 | Dec 26 |
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: Belleville Siu Rsch, Il, about 13.4 miles away@if(!empty($station['elevation_ft'])), at 450 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 St. Jacob, IL?
On average, the last spring frost (32°F) around St. Jacob, IL is about Apr 12. In cooler years it can run later, so for a safer bet many gardeners wait until Mar 28.
When is the first frost in the fall?
The first fall frost around St. Jacob, IL typically arrives about Oct 20. 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 12 on average, or Mar 28 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 189 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 62281 Planting calendar → Illinois frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026