Freeport, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 37.9 °F (low) to 57.9 °F (high). Annual precipitation averages 38.3 Inches. 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 | 11.8 °F | 28.5 °F | 1.54 in. |
| February | 15.2 °F | 32.8 °F | 1.68 in. |
| March | 25.8 °F | 45.1 °F | 2.08 in. |
| April | 36.4 °F | 58.7 °F | 3.64 in. |
| May | 48.2 °F | 70.2 °F | 4.44 in. |
| June | 58.2 °F | 79.5 °F | 5.45 in. |
| July | 61.7 °F | 82.4 °F | 4.46 in. |
| August | 59.6 °F | 80.9 °F | 3.92 in. |
| September | 51.0 °F | 74.6 °F | 4.11 in. |
| October | 39.6 °F | 61.9 °F | 2.89 in. |
| November | 28.6 °F | 46.6 °F | 2.24 in. |
| December | 18.2 °F | 33.9 °F | 1.87 in. |
| Annual | 37.9 °F | 57.9 °F | 38.32 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |