Hillsboro, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.8 °C (low) to 18 °C (high). Annual precipitation averages 1068.1 Millimeters. 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 | -6.3 °C | 2.4 °C | 70.87 mm |
| February | -4.2 °C | 5.4 °C | 56.9 mm |
| March | 0.7 °C | 11.6 °C | 77.98 mm |
| April | 6.4 °C | 18.7 °C | 125.98 mm |
| May | 12.4 °C | 24.2 °C | 131.57 mm |
| June | 17.4 °C | 29 °C | 110.74 mm |
| July | 19.2 °C | 30.7 °C | 97.03 mm |
| August | 17.9 °C | 30 °C | 83.06 mm |
| September | 13.3 °C | 26.8 °C | 75.18 mm |
| October | 6.9 °C | 20.1 °C | 85.09 mm |
| November | 1.4 °C | 11.7 °C | 88.39 mm |
| December | -3.5 °C | 5.2 °C | 65.28 mm |
| Annual | 6.8 °C | 18 °C | 1068.07 mm |
| 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 : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |