Hillsdale, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.9 °C (low) to 15.6 °C (high). Annual precipitation averages 978.7 Millimeters. Hillsdale 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 | -9.9 °C | -1 °C | 40.89 mm |
| February | -7.9 °C | 1.5 °C | 45.47 mm |
| March | -1.9 °C | 8.7 °C | 63.75 mm |
| April | 4.2 °C | 16.2 °C | 95 mm |
| May | 10.8 °C | 22.4 °C | 122.17 mm |
| June | 16.3 °C | 27.6 °C | 124.71 mm |
| July | 18.3 °C | 29.3 °C | 107.95 mm |
| August | 17.1 °C | 28.2 °C | 103.63 mm |
| September | 12.5 °C | 24.8 °C | 90.93 mm |
| October | 5.9 °C | 17.7 °C | 73.66 mm |
| November | -0.6 °C | 9.2 °C | 58.93 mm |
| December | -6.4 °C | 2.1 °C | 51.56 mm |
| Annual | 4.9 °C | 15.6 °C | 978.65 mm |
| 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 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |