Millstadt, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.6 °C (low) to 19.1 °C (high). Annual precipitation averages 1142 Millimeters. Millstadt 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 | -4.5 °C | 4.6 °C | 70.61 mm |
| February | -2.6 °C | 7.6 °C | 61.98 mm |
| March | 2.3 °C | 13.2 °C | 91.44 mm |
| April | 8.2 °C | 19.9 °C | 124.46 mm |
| May | 14.1 °C | 24.7 °C | 131.32 mm |
| June | 18.9 °C | 29.7 °C | 124.71 mm |
| July | 21.1 °C | 31.4 °C | 109.22 mm |
| August | 20.1 °C | 30.7 °C | 92.96 mm |
| September | 15.6 °C | 27.1 °C | 85.6 mm |
| October | 9.4 °C | 20.7 °C | 82.55 mm |
| November | 2.9 °C | 12.9 °C | 93.73 mm |
| December | -1.8 °C | 7 °C | 73.41 mm |
| Annual | 8.6 °C | 19.1 °C | 1141.99 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 |