Cook County Climate
Cook County, Illinois
Avg Annual Temp
50.3°F
Annual Precip
38.6"
Annual Snowfall
33.6"
Extreme Heat Days
20.3375
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Cook County Weather
Much cooler than the national temperature median
Cook County’s annual average of 50.3°F is significantly cooler than the national median. This reflects its northern position and the cooling influence of the Great Lakes.
One of the coolest counties in Illinois
Cook is one of the coolest counties in the state, sitting 2.5 degrees below the Illinois average of 52.8°F. It receives less rain than the state average but experiences much more snowfall.
The snowiest county in the region
With 33.6 inches of snow, Cook is the snowiest county in this set, more than doubling the accumulation of Coles County. Its 20 extreme heat days are the lowest among these eight counties.
Severe winters and lake-tempered summers
Winters are cold and snowy, with a January average of 24.1°F and over 33 inches of snow. Summers are tempered by Lake Michigan, resulting in a mild July average of 74.4°F and relatively few 90-degree days.
Prepare for heavy snow and cold winters
Heavy-duty snow blowers and high-quality winter coats are essential for the 33.6 inches of annual snow. Energy-efficient heating is a priority for the 27.1°F winter average, while summers remain generally mild.
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.