Stillman Valley, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.7 °F (low) to 58.1 °F (high). Annual precipitation averages 37.8 Inches. Stillman Valley 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 | 12.3 °F | 28.6 °F | 1.65 in. |
| February | 15.7 °F | 32.7 °F | 1.68 in. |
| March | 26.5 °F | 45.2 °F | 2.22 in. |
| April | 37.5 °F | 59.0 °F | 3.7 in. |
| May | 49.2 °F | 70.4 °F | 4.59 in. |
| June | 59.2 °F | 79.7 °F | 5.27 in. |
| July | 62.7 °F | 82.7 °F | 4.21 in. |
| August | 60.7 °F | 81.3 °F | 4.1 in. |
| September | 52.2 °F | 75.0 °F | 3.41 in. |
| October | 40.5 °F | 62.1 °F | 2.88 in. |
| November | 29.2 °F | 46.9 °F | 2.19 in. |
| December | 18.7 °F | 34.1 °F | 1.86 in. |
| Annual | 38.7 °F | 58.1 °F | 37.76 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 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |