Iroquois, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 1.4 °C (low) to 13.7 °C (high). Annual precipitation averages 605.8 Millimeters. Iroquois is located in USDA Plant Hardiness Zone 4b. 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 | -14.5 °C | -3.8 °C | 13.97 mm |
| February | -12.2 °C | -0.8 °C | 17.27 mm |
| March | -5.9 °C | 5.9 °C | 27.18 mm |
| April | 0.7 °C | 14.1 °C | 62.23 mm |
| May | 7.7 °C | 20.7 °C | 78.74 mm |
| June | 13.8 °C | 26.3 °C | 96.77 mm |
| July | 16.3 °C | 29.3 °C | 82.55 mm |
| August | 15 °C | 28.2 °C | 74.42 mm |
| September | 10 °C | 23.9 °C | 62.99 mm |
| October | 2.2 °C | 15.7 °C | 50.8 mm |
| November | -5.3 °C | 6.4 °C | 21.08 mm |
| December | -11.6 °C | -1.2 °C | 17.78 mm |
| Annual | 1.4 °C | 13.7 °C | 605.78 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 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |