DeKalb, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.5 °F (low) to 58.1 °F (high). Annual precipitation averages 37 Inches. DeKalb 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 | 12.8 °F | 28.6 °F | 1.7 in. |
| February | 16.3 °F | 32.8 °F | 1.73 in. |
| March | 26.3 °F | 45.1 °F | 2.22 in. |
| April | 36.8 °F | 58.6 °F | 3.44 in. |
| May | 48.6 °F | 70.1 °F | 4.9 in. |
| June | 58.5 °F | 79.7 °F | 4.58 in. |
| July | 62.3 °F | 82.7 °F | 3.82 in. |
| August | 60.1 °F | 80.9 °F | 3.95 in. |
| September | 51.7 °F | 75.0 °F | 3.37 in. |
| October | 40.0 °F | 62.2 °F | 2.97 in. |
| November | 29.4 °F | 46.9 °F | 2.37 in. |
| December | 18.9 °F | 34.1 °F | 1.98 in. |
| Annual | 38.5 °F | 58.1 °F | 37.03 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |