Weather in Cook County, Illinois for September 2025
Until now, September 2025 in Cook County is cooler than usual, with temperatures averaging 22 °F, this is -3.1 °F below the typical seasonal average.
The forecast for the next days in Cook County predicts temperatures to be around 25 °F, close to the historical average.
In general, the average temperature in Cook County at the beginning of September is 25.4 °F. As the month progressed, temperatures tended to moderately fall, reaching an average of 23.7 °F by the end of September.
The climate of Cook County in September is notably wet, with an average of 13 rainy days, and a total of 71.9 mm of precipitation.
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Cook County Weather September
Temperatures trend during September in Cook County
September weather in Cook County day by day
| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 26° /18° | 0 mm | 6 | |
| Sept. 2 |  Partly cloudy | 26° /19° | 0 mm | 6 | |
| Sept. 3 |  Moderate rain at times | 27° /17° | 8.4 mm | 6 | |
| Sept. 4 | Moderate rain at times | 25° /18° | 0.4 mm | 6 | |
| Sept. 5 | Sunny | 27° /18° | 0.2 mm | 6 | |
| Sept. 6 |  Patchy rain possible | 24° /17° | 2.3 mm | 6 | |
| Sept. 7 | Patchy rain possible | 23° /15° | 3 mm | 5 | |
| Sept. 8 | Sunny | 24° /15° | 0 mm | 6 | |
| Sept. 9 | Sunny | 25° /16° | 0 mm | 6 | |
| Sept. 10 | Sunny | 26° /17° | 0 mm | 6 | |
| Sept. 11 |  Cloudy | 25° /17° | 20.3 mm | 6 | |
| Sept. 12 | Partly cloudy | 23° /16° | 0.1 mm | 5 | |
| Sept. 13 | Light rain shower | 25° /17° | 2.2 mm | 5 | |
| Sept. 14 | Sunny | 25° /18° | 0.6 mm | 6 | |
| Sept. 15 | Cloudy | 27° /18° | 0 mm | 6 | |
| Sept. 16 | Partly cloudy | 25° /17° | 0 mm | 1.5 | |
| Sept. 17 | Partly cloudy | 25° /16° | 0 mm | 1.5 | |
| Sept. 18 |  Mist | 28° /16° | 0 mm | 1.4 | |
| Sept. 19 | Sunny | 28° /19° | 0 mm | 1.3 | |
| Sept. 20 | Patchy rain possible | 24° /19° | 4.2 mm | 0 | |
| Sept. 21 | Patchy rain possible | 26° /19° | 4.6 mm | 5 | |
| Sept. 22 | Patchy rain possible | 30° /21° | 1.5 mm | 5 | |
| Sept. 23 | Patchy rain possible | 23° /18° | 0.8 mm | 5 | |
| Sept. 24 | Sunny | 28° /19° | 0 mm | 6 | |
| Sept. 25 | Sunny | 23° /19° | 0 mm | 6 | |
| Sept. 26 | Sunny | 18° /15° | 0 mm | 5 | |
| Sept. 27 | Sunny | 21° /14° | 0 mm | 5 | |
| Sept. 28 | Sunny | 26° /16° | 0 mm | 6 | |
| Sept. 29 | Sunny | 28° /17° | 0 mm | 6 | |
| Sept. 30 | Sunny | 22° /16° | 0 mm | 6 | |
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Cook County in September - FAQ
September rainfall patterns in Cook County
UV exposure in Cook County during September
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Where is Cook County?Get accurate weather forecasts for Cook County, located at latitude 41.85 and longitude -87.65. Stay updated with localized weather information tailored for Cook County.