Mill Creek, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.5 °C (low) to 19.8 °C (high). Annual precipitation averages 1265.2 Millimeters. 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 | -3.7 °C | 5.8 °C | 93.22 mm |
| February | -1.8 °C | 8.7 °C | 88.14 mm |
| March | 2.7 °C | 14.1 °C | 118.62 mm |
| April | 8.2 °C | 20.3 °C | 137.67 mm |
| May | 13.8 °C | 25.2 °C | 138.18 mm |
| June | 18.6 °C | 29.9 °C | 113.54 mm |
| July | 20.6 °C | 31.6 °C | 98.3 mm |
| August | 19.2 °C | 30.9 °C | 76.96 mm |
| September | 14.7 °C | 27.7 °C | 86.36 mm |
| October | 8.2 °C | 21.8 °C | 97.03 mm |
| November | 2.7 °C | 14.1 °C | 114.81 mm |
| December | -1.6 °C | 7.8 °C | 102.36 mm |
| Annual | 8.5 °C | 19.8 °C | 1265.19 mm |
| 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 : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |