Hartland, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.3 °F (low) to 57.9 °F (high). Annual precipitation averages 38.3 Inches. Hartland is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 13.6 °F | 29.2 °F | 1.72 in. |
| February | 16.3 °F | 33.3 °F | 1.83 in. |
| March | 25.8 °F | 44.9 °F | 2.28 in. |
| April | 36.0 °F | 57.9 °F | 3.81 in. |
| May | 47.6 °F | 69.6 °F | 4.6 in. |
| June | 57.3 °F | 79.1 °F | 5.05 in. |
| July | 61.6 °F | 82.8 °F | 3.97 in. |
| August | 59.8 °F | 81.2 °F | 3.95 in. |
| September | 52.0 °F | 74.5 °F | 3.63 in. |
| October | 40.7 °F | 61.4 °F | 2.95 in. |
| November | 29.9 °F | 46.7 °F | 2.44 in. |
| December | 19.4 °F | 34.1 °F | 2.02 in. |
| Annual | 38.3 °F | 57.9 °F | 38.25 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |