Stephenson County Climate
Stephenson County, Illinois
Avg Annual Temp
47.7°F
Annual Precip
38.4"
Annual Snowfall
34.5"
Extreme Heat Days
10.6
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Stephenson County Weather
A Cold Northern Climate
Stephenson County’s 47.7°F annual average is much lower than the national median of 52.7°F. This northern Illinois region experiences a true continental climate.
Well Below the State Average
The county is one of the coldest in Illinois, sitting five degrees below the state average of 52.8°F. It also records less rain than the state norm, with 38.4 inches annually.
Northern Chills Compared to Central IL
Stephenson is nearly six degrees cooler than Sangamon County on average. It receives 34.5 inches of snow, more than double the amount found in southern Illinois counties.
Brutal Winters and Mild Summers
Winter temperatures average a frigid 23.0°F, bringing heavy snowfall of 34.5 inches. Summers are pleasant, with only 11 days of extreme heat and a July average of 72.4°F.
Winter Readiness is Key
Residents must own heavy-duty snow removal equipment and ensure homes are well-insulated against the 23°F winter average. Air conditioning needs are lower here than in the rest of the state.
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.