Climate change in Cook County, Illinois
Since 1979, Cook County, Illinois has warmed 2.8°F, with 2 more days above 90°F, 3 more nights above 70°F and 2% more precipitation a year. Its climate in 1996–2025 is most like Ottawa County, OH's was in 1951–1980.
- Average temperature: +2.8°F
- Summer highs (Jun–Aug): +1.7°F
- Winter lows (Dec–Feb): +4.3°F
- Precipitation: +2%
- Wettest day of the year: +3%
- Longest dry spell: −4 days
- Days above 90°F: +2 days
- Nights above 70°F: +3 days
- Freezing nights: −14 days
- Frost-free season: +13 days
- Muggy days: +5 days
- Summer heat index (Jun–Aug): +2.2°F
- Extreme fire-weather days: +14 days
- Snowfall: +3%
- Snowy days (1 inch or more): −0 days
Changes follow the trend line through every year from 1979 to 2025. Data: NOAA nClimGrid-Daily; humidity from gridMET, adjusted to airport observations.