Maryville, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 47.4 °F (low) to 66.1 °F (high). Annual precipitation averages 44.7 Inches. 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 | 23.8 °F | 39.8 °F | 2.7 in. |
| February | 27.0 °F | 45.3 °F | 2.42 in. |
| March | 35.9 °F | 55.6 °F | 3.49 in. |
| April | 46.6 °F | 67.1 °F | 4.95 in. |
| May | 57.5 °F | 76.2 °F | 5.24 in. |
| June | 66.4 °F | 84.9 °F | 4.8 in. |
| July | 70.1 °F | 88.0 °F | 4.33 in. |
| August | 68.1 °F | 87.0 °F | 3.86 in. |
| September | 59.8 °F | 80.6 °F | 3.23 in. |
| October | 48.7 °F | 69.1 °F | 3.29 in. |
| November | 36.8 °F | 54.9 °F | 3.64 in. |
| December | 28.5 °F | 44.3 °F | 2.75 in. |
| Annual | 47.4 °F | 66.1 °F | 44.7 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 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |