Mount Carroll, Illinois has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.3 °C (low) to 15 °C (high). Annual precipitation averages 991.4 Millimeters. Mount Carroll is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.2 °C | -1.6 °C | 39.88 mm |
| February | -9.2 °C | 0.9 °C | 44.7 mm |
| March | -3.3 °C | 7.8 °C | 60.71 mm |
| April | 2.6 °C | 15.4 °C | 96.52 mm |
| May | 9.1 °C | 22 °C | 115.57 mm |
| June | 14.6 °C | 27.1 °C | 137.41 mm |
| July | 16.4 °C | 28.7 °C | 119.13 mm |
| August | 15.2 °C | 27.9 °C | 99.31 mm |
| September | 10.4 °C | 24.4 °C | 92.46 mm |
| October | 4.1 °C | 17.3 °C | 73.91 mm |
| November | -2 °C | 8.6 °C | 59.94 mm |
| December | -7.7 °C | 1.4 °C | 51.82 mm |
| Annual | 3.3 °C | 15 °C | 991.36 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |