Keyesport, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.4 °C (low) to 18.5 °C (high). Annual precipitation averages 1120.9 Millimeters. Keyesport is located in USDA Plant Hardiness Zone 6b. 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 | -5.7 °C | 3.6 °C | 74.17 mm |
| February | -3.9 °C | 6.4 °C | 62.74 mm |
| March | 1.3 °C | 12.3 °C | 87.63 mm |
| April | 7.1 °C | 19.1 °C | 120.4 mm |
| May | 13.1 °C | 24.1 °C | 128.27 mm |
| June | 18 °C | 29.1 °C | 121.41 mm |
| July | 19.8 °C | 30.9 °C | 104.39 mm |
| August | 18.6 °C | 30.4 °C | 86.36 mm |
| September | 13.9 °C | 26.8 °C | 85.6 mm |
| October | 7.4 °C | 20.2 °C | 84.07 mm |
| November | 1.7 °C | 12.4 °C | 93.47 mm |
| December | -3.1 °C | 6.1 °C | 72.39 mm |
| Annual | 7.4 °C | 18.5 °C | 1120.9 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°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 |