Sleepy Hollow, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.1 °C (low) to 14.9 °C (high). Annual precipitation averages 1005.3 Millimeters. Sleepy Hollow 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 | -9.7 °C | -0.9 °C | 49.53 mm |
| February | -8.2 °C | 1.3 °C | 46.99 mm |
| March | -2.8 °C | 7.7 °C | 57.4 mm |
| April | 2.9 °C | 14.8 °C | 97.03 mm |
| May | 9 °C | 21.2 °C | 131.57 mm |
| June | 14.6 °C | 26.7 °C | 121.16 mm |
| July | 17.3 °C | 28.9 °C | 101.85 mm |
| August | 16.4 °C | 27.8 °C | 105.41 mm |
| September | 11.9 °C | 24.1 °C | 90.42 mm |
| October | 5.4 °C | 16.8 °C | 84.07 mm |
| November | -0.8 °C | 8.7 °C | 64.77 mm |
| December | -6.3 °C | 2 °C | 55.12 mm |
| Annual | 4.1 °C | 14.9 °C | 1005.32 mm |
| 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 : -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 |