Fairmont City, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 47.1 °F (low) to 66.5 °F (high). Annual precipitation averages 45.1 Inches. Fairmont City is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 23.5 °F | 40.1 °F | 2.7 in. |
| February | 27.0 °F | 45.5 °F | 2.42 in. |
| March | 35.7 °F | 55.5 °F | 3.52 in. |
| April | 46.5 °F | 67.6 °F | 4.83 in. |
| May | 57.1 °F | 76.6 °F | 5.3 in. |
| June | 66.1 °F | 85.5 °F | 4.89 in. |
| July | 69.8 °F | 89.0 °F | 4.39 in. |
| August | 67.9 °F | 87.6 °F | 3.93 in. |
| September | 59.4 °F | 81.0 °F | 3.38 in. |
| October | 47.8 °F | 69.7 °F | 3.27 in. |
| November | 36.9 °F | 55.7 °F | 3.68 in. |
| December | 27.9 °F | 44.5 °F | 2.8 in. |
| Annual | 47.1 °F | 66.5 °F | 45.11 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |