Maryville, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 8.6 °C (low) to 18.9 °C (high). Annual precipitation averages 1135.4 Millimeters. Maryville 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 | -4.6 °C | 4.3 °C | 68.58 mm |
| February | -2.8 °C | 7.4 °C | 61.47 mm |
| March | 2.2 °C | 13.1 °C | 88.65 mm |
| April | 8.1 °C | 19.5 °C | 125.73 mm |
| May | 14.2 °C | 24.6 °C | 133.1 mm |
| June | 19.1 °C | 29.4 °C | 121.92 mm |
| July | 21.2 °C | 31.1 °C | 109.98 mm |
| August | 20.1 °C | 30.6 °C | 98.04 mm |
| September | 15.4 °C | 27 °C | 82.04 mm |
| October | 9.3 °C | 20.6 °C | 83.57 mm |
| November | 2.7 °C | 12.7 °C | 92.46 mm |
| December | -1.9 °C | 6.8 °C | 69.85 mm |
| Annual | 8.6 °C | 18.9 °C | 1135.39 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 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |