Freeport, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.3 °C (low) to 14.4 °C (high). Annual precipitation averages 973.3 Millimeters. Freeport is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.2 °C | -1.9 °C | 39.12 mm |
| February | -9.3 °C | 0.4 °C | 42.67 mm |
| March | -3.4 °C | 7.3 °C | 52.83 mm |
| April | 2.4 °C | 14.8 °C | 92.46 mm |
| May | 9 °C | 21.2 °C | 112.78 mm |
| June | 14.6 °C | 26.4 °C | 138.43 mm |
| July | 16.5 °C | 28 °C | 113.28 mm |
| August | 15.3 °C | 27.2 °C | 99.57 mm |
| September | 10.6 °C | 23.7 °C | 104.39 mm |
| October | 4.2 °C | 16.6 °C | 73.41 mm |
| November | -1.9 °C | 8.1 °C | 56.9 mm |
| December | -7.7 °C | 1.1 °C | 47.5 mm |
| Annual | 3.3 °C | 14.4 °C | 973.34 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |