Eureka, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.9 °F (low) to 61.7 °F (high). Annual precipitation averages 38.1 Inches. Eureka is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.8 °F | 32.5 °F | 2.18 in. |
| February | 19.3 °F | 37.4 °F | 1.97 in. |
| March | 28.9 °F | 49.6 °F | 2.63 in. |
| April | 39.6 °F | 62.9 °F | 3.71 in. |
| May | 51.2 °F | 73.5 °F | 4.52 in. |
| June | 60.9 °F | 82.2 °F | 4.4 in. |
| July | 64.1 °F | 85.4 °F | 3.71 in. |
| August | 62.0 °F | 83.7 °F | 3.56 in. |
| September | 53.9 °F | 78.9 °F | 3.44 in. |
| October | 42.4 °F | 65.8 °F | 3.14 in. |
| November | 31.3 °F | 50.5 °F | 2.72 in. |
| December | 21.6 °F | 37.8 °F | 2.1 in. |
| Annual | 40.9 °F | 61.7 °F | 38.08 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°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 |