Smithton, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.3 °C (low) to 19.2 °C (high). Annual precipitation averages 1132.8 Millimeters. Smithton is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.8 °C | 4.6 °C | 70.1 mm |
| February | -2.8 °C | 7.6 °C | 62.23 mm |
| March | 1.9 °C | 13.2 °C | 90.17 mm |
| April | 7.9 °C | 19.8 °C | 126.75 mm |
| May | 13.8 °C | 24.8 °C | 130.3 mm |
| June | 18.8 °C | 29.7 °C | 123.44 mm |
| July | 20.8 °C | 31.6 °C | 106.43 mm |
| August | 19.7 °C | 30.9 °C | 89.92 mm |
| September | 15.1 °C | 27.3 °C | 83.82 mm |
| October | 8.7 °C | 20.9 °C | 80.26 mm |
| November | 2.5 °C | 13.1 °C | 95 mm |
| December | -2.3 °C | 7 °C | 74.42 mm |
| Annual | 8.3 °C | 19.2 °C | 1132.84 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |