Frankfort, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41.3 °F (low) to 60.1 °F (high). Annual precipitation averages 40.5 Inches. 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 | 16.6 °F | 32.1 °F | 2.2 in. |
| February | 19.3 °F | 36.0 °F | 2.13 in. |
| March | 28.7 °F | 47.3 °F | 2.43 in. |
| April | 39.3 °F | 60.0 °F | 3.91 in. |
| May | 50.0 °F | 70.8 °F | 4.67 in. |
| June | 60.0 °F | 80.8 °F | 4.65 in. |
| July | 64.8 °F | 84.7 °F | 4.62 in. |
| August | 63.0 °F | 82.8 °F | 4.17 in. |
| September | 55.5 °F | 76.6 °F | 3.42 in. |
| October | 43.1 °F | 63.1 °F | 3.43 in. |
| November | 32.5 °F | 49.4 °F | 2.6 in. |
| December | 22.2 °F | 37.0 °F | 2.23 in. |
| Annual | 41.3 °F | 60.1 °F | 40.46 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |