Smithfield, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41.2 °F (low) to 61.8 °F (high). Annual precipitation averages 38.8 Inches. Smithfield 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.7 °F | 32.8 °F | 1.89 in. |
| February | 19.2 °F | 37.4 °F | 1.92 in. |
| March | 29.4 °F | 50.0 °F | 2.51 in. |
| April | 40.1 °F | 63.1 °F | 3.87 in. |
| May | 52.0 °F | 73.6 °F | 5.06 in. |
| June | 61.6 °F | 82.4 °F | 4.78 in. |
| July | 64.7 °F | 85.6 °F | 4.03 in. |
| August | 62.4 °F | 84.0 °F | 3.53 in. |
| September | 54.2 °F | 78.3 °F | 3.61 in. |
| October | 42.3 °F | 65.8 °F | 3.04 in. |
| November | 31.1 °F | 50.5 °F | 2.56 in. |
| December | 21.6 °F | 38.0 °F | 2.03 in. |
| Annual | 41.2 °F | 61.8 °F | 38.83 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| 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 |