Frost dates for Hillsboro, IL
At Hillsboro, the median last spring frost (32°F) is Apr 13 and the median first fall frost is Oct 24, for a typical growing season of 192 days. For a 90% chance that the last frost has passed, wait until Apr 28. Nearby ZIP codes are in USDA hardiness zone 6b.
- Apr 13Last spring frost (median)50% chance of 32°F after this date
- Apr 28Safer planting date10% chance of 32°F after this date
- Oct 24First fall frost (median)50% chance of 32°F by this date
- 192 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Apr 9 | Apr 24 | May 11 |
| 32°F | Mar 30 | Apr 13 | Apr 28 |
| 28°F | Mar 17 | Apr 2 | Apr 18 |
| 24°F | Mar 3 | Mar 22 | Apr 5 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Sep 27 | Oct 13 | Oct 26 |
| 32°F | Oct 10 | Oct 24 | Nov 4 |
| 28°F | Oct 21 | Nov 2 | Nov 20 |
| 24°F | Nov 1 | Nov 13 | Dec 2 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 148 days | 170 days | 189 days |
| 32°F | 170 days | 192 days | 212 days |
| 28°F | 192 days | 214 days | 237 days |
| 24°F | 215 days | 236 days | 261 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 62049 | 6b | -5 to 0°F | 2 km |
| 62089 | 6b | -5 to 0°F | 5 km |
| 62015 | 6b | -5 to 0°F | 7 km |
| 62051 | 6b | -5 to 0°F | 9 km |
| 62077 | 6b | -5 to 0°F | 14 km |
| 62094 | 6b | -5 to 0°F | 15 km |
| 62017 | 6b | -5 to 0°F | 15 km |
| 62091 | 6b | -5 to 0°F | 16 km |
| 62056 | 6b | -5 to 0°F | 16 km |
| 62019 | 6b | -5 to 0°F | 16 km |
| 62086 | 6b | -5 to 0°F | 21 km |
| 62069 | 6b | -5 to 0°F | 23 km |
| 62074 | 6b | -5 to 0°F | 29 km |
| 62058 | 6b | -5 to 0°F | 32 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00114108, at 39.1611, -89.4919, elevation 192 m (630 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 100.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Morrisonville (28 km)
- Ramsey (34 km)
- Carlinville (36 km)
- Vandalia (41 km)
- Pana (42 km)
- Virden (45 km)
- Brownstown 4 SW (51 km)
- Carlyle Rsvr (61 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.