Fillmore, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.5 °C (low) to 17.8 °C (high). Annual precipitation averages 1076.5 Millimeters. Fillmore is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.6 °C | 2.3 °C | 70.61 mm |
| February | -4.6 °C | 5.3 °C | 57.91 mm |
| March | 0.4 °C | 11.4 °C | 79.76 mm |
| April | 6.1 °C | 18.4 °C | 119.63 mm |
| May | 12.2 °C | 23.9 °C | 124.46 mm |
| June | 17.2 °C | 28.8 °C | 115.06 mm |
| July | 18.9 °C | 30.4 °C | 102.11 mm |
| August | 17.6 °C | 29.8 °C | 84.58 mm |
| September | 13.1 °C | 26.8 °C | 80.01 mm |
| October | 6.7 °C | 19.9 °C | 85.85 mm |
| November | 1.1 °C | 11.6 °C | 89.92 mm |
| December | -3.7 °C | 5.1 °C | 66.55 mm |
| Annual | 6.5 °C | 17.8 °C | 1076.45 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |