Wilmington, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.7 °C (low) to 15.8 °C (high). Annual precipitation averages 984 Millimeters. Wilmington is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9 °C | -0.1 °C | 54.36 mm |
| February | -7.4 °C | 2.2 °C | 48.51 mm |
| March | -2.1 °C | 8.8 °C | 60.45 mm |
| April | 3.7 °C | 16.1 °C | 95.25 mm |
| May | 10 °C | 22.2 °C | 119.63 mm |
| June | 15.6 °C | 27.5 °C | 117.09 mm |
| July | 17.5 °C | 29.3 °C | 106.68 mm |
| August | 16.4 °C | 28.3 °C | 99.31 mm |
| September | 12.1 °C | 25.3 °C | 85.09 mm |
| October | 5.6 °C | 17.9 °C | 80.01 mm |
| November | -0.3 °C | 9.7 °C | 63.75 mm |
| December | -5.7 °C | 2.8 °C | 53.85 mm |
| Annual | 4.7 °C | 15.8 °C | 983.98 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |