Jefferson County Climate
Jefferson County, Illinois
Avg Annual Temp
54.5°F
Annual Precip
44.9"
Annual Snowfall
9.5"
Extreme Heat Days
20.7
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Jefferson County Weather
Warmer than the national median temperature
Jefferson's 54.5°F average temperature is higher than the national median of 53°F. It experiences a relatively wet climate with 44.9 inches of rain.
Exceeding the Illinois state temperature average
At 54.5°F, the county is 1.7°F warmer than the Illinois state average of 52.8°F. It sits firmly in the warmer southern half of the state.
Much less snow than northern Henry County
Jefferson sees only 9.5 inches of snow, nearly 20 inches less than Henry County. Its precipitation is also higher than the state average of 41.7 inches.
Warm summers with three weeks of heat
July averages 76.5°F, including 21 days of extreme heat above 90°F. Winters are relatively mild, with January temperatures averaging 30.1°F.
Focus on cooling and heavy rain management
Efficient air conditioning is key for the 21 extreme heat days. Residents should also be prepared for 44.9 inches of rain with proper roof and gutter care.
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.