Hillsboro, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 44.3 °F (low) to 64.4 °F (high). Annual precipitation averages 42.1 Inches. Hillsboro is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 20.6 °F | 36.4 °F | 2.79 in. |
| February | 24.4 °F | 41.8 °F | 2.24 in. |
| March | 33.3 °F | 52.8 °F | 3.07 in. |
| April | 43.6 °F | 65.6 °F | 4.96 in. |
| May | 54.4 °F | 75.5 °F | 5.18 in. |
| June | 63.3 °F | 84.2 °F | 4.36 in. |
| July | 66.5 °F | 87.2 °F | 3.82 in. |
| August | 64.2 °F | 86.0 °F | 3.27 in. |
| September | 56.0 °F | 80.3 °F | 2.96 in. |
| October | 44.5 °F | 68.2 °F | 3.35 in. |
| November | 34.6 °F | 53.1 °F | 3.48 in. |
| December | 25.7 °F | 41.3 °F | 2.57 in. |
| Annual | 44.3 °F | 64.4 °F | 42.05 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°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 |