Stonington, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 43 °F (low) to 63.5 °F (high). Annual precipitation averages 39.9 Inches. Stonington is located in USDA Plant Hardiness Zone 6a. 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 | 19.1 °F | 35.5 °F | 2.22 in. |
| February | 22.3 °F | 40.5 °F | 2.02 in. |
| March | 31.5 °F | 51.7 °F | 2.8 in. |
| April | 42.1 °F | 64.7 °F | 4.29 in. |
| May | 53.4 °F | 74.9 °F | 4.66 in. |
| June | 62.4 °F | 83.3 °F | 4.68 in. |
| July | 65.3 °F | 86.3 °F | 3.79 in. |
| August | 63.2 °F | 84.9 °F | 3.36 in. |
| September | 55.0 °F | 80.0 °F | 3.22 in. |
| October | 43.6 °F | 67.6 °F | 3.3 in. |
| November | 33.1 °F | 52.2 °F | 3.23 in. |
| December | 24.6 °F | 40.4 °F | 2.35 in. |
| Annual | 43 °F | 63.5 °F | 39.92 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 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |