Mount Carroll, Illinois has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 37.8 °F (low) to 59 °F (high). Annual precipitation averages 39 Inches. 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 | 11.8 °F | 29.2 °F | 1.57 in. |
| February | 15.5 °F | 33.7 °F | 1.76 in. |
| March | 26.0 °F | 46.0 °F | 2.39 in. |
| April | 36.6 °F | 59.8 °F | 3.8 in. |
| May | 48.3 °F | 71.6 °F | 4.55 in. |
| June | 58.2 °F | 80.8 °F | 5.41 in. |
| July | 61.6 °F | 83.7 °F | 4.69 in. |
| August | 59.3 °F | 82.2 °F | 3.91 in. |
| September | 50.8 °F | 76.0 °F | 3.64 in. |
| October | 39.4 °F | 63.1 °F | 2.91 in. |
| November | 28.4 °F | 47.4 °F | 2.36 in. |
| December | 18.1 °F | 34.6 °F | 2.04 in. |
| Annual | 37.8 °F | 59 °F | 39.03 in. |
| 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 : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |