Mill Creek, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 47.2 °F (low) to 67.7 °F (high). Annual precipitation averages 49.8 Inches. Mill Creek is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 25.3 °F | 42.4 °F | 3.67 in. |
| February | 28.7 °F | 47.7 °F | 3.47 in. |
| March | 36.8 °F | 57.4 °F | 4.67 in. |
| April | 46.7 °F | 68.6 °F | 5.42 in. |
| May | 56.9 °F | 77.4 °F | 5.44 in. |
| June | 65.5 °F | 85.9 °F | 4.47 in. |
| July | 69.0 °F | 88.8 °F | 3.87 in. |
| August | 66.5 °F | 87.7 °F | 3.03 in. |
| September | 58.5 °F | 81.9 °F | 3.4 in. |
| October | 46.7 °F | 71.2 °F | 3.82 in. |
| November | 36.8 °F | 57.3 °F | 4.52 in. |
| December | 29.2 °F | 46.1 °F | 4.03 in. |
| Annual | 47.2 °F | 67.7 °F | 49.81 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |