Frankfort, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.2 °C (low) to 15.6 °C (high). Annual precipitation averages 1027.7 Millimeters. Frankfort is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.6 °C | 0.1 °C | 55.88 mm |
| February | -7.1 °C | 2.2 °C | 54.1 mm |
| March | -1.8 °C | 8.5 °C | 61.72 mm |
| April | 4.1 °C | 15.6 °C | 99.31 mm |
| May | 10 °C | 21.6 °C | 118.62 mm |
| June | 15.6 °C | 27.1 °C | 118.11 mm |
| July | 18.2 °C | 29.3 °C | 117.35 mm |
| August | 17.2 °C | 28.2 °C | 105.92 mm |
| September | 13.1 °C | 24.8 °C | 86.87 mm |
| October | 6.2 °C | 17.3 °C | 87.12 mm |
| November | 0.3 °C | 9.7 °C | 66.04 mm |
| December | -5.4 °C | 2.8 °C | 56.64 mm |
| Annual | 5.2 °C | 15.6 °C | 1027.68 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |