Casey, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 43.8 °F (low) to 64.1 °F (high). Annual precipitation averages 43.9 Inches. Casey is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 20.8 °F | 36.8 °F | 3.03 in. |
| February | 23.6 °F | 41.8 °F | 2.54 in. |
| March | 32.6 °F | 52.6 °F | 3.15 in. |
| April | 43.0 °F | 65.2 °F | 4.92 in. |
| May | 54.0 °F | 74.9 °F | 4.63 in. |
| June | 62.8 °F | 83.4 °F | 4.92 in. |
| July | 65.6 °F | 86.6 °F | 4.24 in. |
| August | 63.5 °F | 85.6 °F | 3.01 in. |
| September | 55.7 °F | 80.2 °F | 3.02 in. |
| October | 44.3 °F | 67.7 °F | 3.7 in. |
| November | 33.9 °F | 53.2 °F | 3.81 in. |
| December | 25.6 °F | 41.3 °F | 2.89 in. |
| Annual | 43.8 °F | 64.1 °F | 43.86 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°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 |