Caseyville, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 47.1 °F (low) to 66.4 °F (high). Annual precipitation averages 45.4 Inches. Caseyville 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 | 23.4 °F | 40.0 °F | 2.75 in. |
| February | 26.8 °F | 45.3 °F | 2.42 in. |
| March | 35.6 °F | 55.5 °F | 3.55 in. |
| April | 46.3 °F | 67.5 °F | 4.91 in. |
| May | 57.1 °F | 76.5 °F | 5.26 in. |
| June | 66.0 °F | 85.3 °F | 5.06 in. |
| July | 69.8 °F | 88.7 °F | 4.47 in. |
| August | 67.8 °F | 87.4 °F | 3.83 in. |
| September | 59.4 °F | 80.9 °F | 3.4 in. |
| October | 47.9 °F | 69.4 °F | 3.26 in. |
| November | 36.7 °F | 55.4 °F | 3.72 in. |
| December | 28.0 °F | 44.4 °F | 2.8 in. |
| Annual | 47.1 °F | 66.4 °F | 45.43 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 | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |