Union County Climate
Union County, Illinois
Avg Annual Temp
58.5°F
Annual Precip
51.1"
Annual Snowfall
10.4"
Extreme Heat Days
43
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Union County Weather
Far Exceeding National Temperatures
Union County averages 58.5°F annually, which is nearly six degrees warmer than the national median. It features a humid subtropical influence unique to the state's southern tip.
Illinois’ Warmest and Wettest Corner
At 58.5°F, this is one of the warmest counties in Illinois, far exceeding the 52.8°F state average. It is also exceptionally wet, receiving 51.1 inches of annual rain.
A Southern Illinois Thermal Peak
Union is even warmer than St. Clair County, which averages 56.8°F. It also receives about eight more inches of rain annually than its northern neighbors.
Long Summers and Little Snow
The county faces 43 days of extreme heat with July temperatures averaging 79.2°F. Winters are the mildest in the state, averaging 37.9°F with only 10.4 inches of snow.
Manage Heat and High Humidity
Residents need high-capacity cooling and dehumidification to handle the 51.1 inches of rain and 43 days of extreme heat. Heavy winter clothing is rarely needed given the mild 37.9°F winter average.
Frequently Asked Questions
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Data source: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020.
Climate normals are 30-year averages of weather variables computed from 1991 to 2020. Station data is aggregated to county level using spatial averaging. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.