Cook County Climate
Cook County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
50.3°F
Annual Precip
38.6"
Annual Snowfall
33.6"
Extreme Heat Days
20
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
6a
Minimum winter temperature range for plant survival
3,161
Supports most vegetables & fruits
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: Cook County
Climate Verdict
Cook County has a mild, with an average annual temperature of 50.3°F, moderate rainfall of 38.6 inches per year, occasional hot days — 20.337500000000002 per year above 90°F, moderate snowfall of 33.6 inches annually. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are very cold — January averages 24.1°F. summers are warm — July averages 74.4°F. Residents experience a substantial 50°F difference between winter and summer.
Outdoor & Gardening Guidance
Growing season and gardening data is currently limited for Cook County. Check the USDA Plant Hardiness Zone Map and local extension office for specific guidance.
Regional Context
Cook County closely matches the Illinois statewide average temperature of 52.8°F, it is somewhat drier than average for Illinois.
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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Track your own weather in Cook County
Ambient Weather personal weather stations give you hyperlocal climate data.
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Data sources: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020. Forecast and alert data from National Weather Service API. Air quality data from Open-Meteo.
Climate normals are 30-year averages of weather variables. Station data is aggregated to county level. Forecasts and alerts are fetched live and may change frequently. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.