De Witt, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41.7 °F (low) to 62.1 °F (high). Annual precipitation averages 39.4 Inches. De Witt 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 | 17.2 °F | 33.6 °F | 2.25 in. |
| February | 20.5 °F | 38.2 °F | 1.98 in. |
| March | 29.5 °F | 49.9 °F | 2.69 in. |
| April | 40.5 °F | 63.5 °F | 3.9 in. |
| May | 52.2 °F | 73.9 °F | 4.45 in. |
| June | 61.4 °F | 82.6 °F | 4.49 in. |
| July | 64.5 °F | 85.3 °F | 4.15 in. |
| August | 62.2 °F | 83.8 °F | 3.44 in. |
| September | 54.6 °F | 78.8 °F | 3.29 in. |
| October | 42.7 °F | 65.8 °F | 3.39 in. |
| November | 31.9 °F | 50.9 °F | 2.93 in. |
| December | 23.0 °F | 38.4 °F | 2.41 in. |
| Annual | 41.7 °F | 62.1 °F | 39.37 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 6a : -10°F to -5°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 |