Farmington, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.3 °F (low) to 60.9 °F (high). Annual precipitation averages 38.4 Inches. Farmington 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 | 14.7 °F | 31.8 °F | 1.93 in. |
| February | 18.2 °F | 36.5 °F | 1.98 in. |
| March | 28.4 °F | 49.2 °F | 2.47 in. |
| April | 39.1 °F | 62.1 °F | 3.69 in. |
| May | 51.1 °F | 72.7 °F | 4.96 in. |
| June | 60.8 °F | 81.6 °F | 4.66 in. |
| July | 63.9 °F | 84.6 °F | 4.11 in. |
| August | 61.7 °F | 83.1 °F | 3.51 in. |
| September | 53.4 °F | 77.4 °F | 3.75 in. |
| October | 41.7 °F | 64.8 °F | 2.88 in. |
| November | 30.2 °F | 49.7 °F | 2.44 in. |
| December | 20.6 °F | 37.2 °F | 1.99 in. |
| Annual | 40.3 °F | 60.9 °F | 38.37 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |