Cook County (Chicago)
September
Weather in Cook County, Illinois for September 2026
Your guide to Cook County weather in September - trends and predictions
In general, the average temperature in Cook County at the beginning of September is 25.4 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 21.9 °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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Temperatures
Rain 🌧️
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17
Dry days
13
Rainy days
0
Snow days
24°/17°
Temperatures
19 km/h
Avg max wind
64 %
Avg humidity
Cook County Weather September
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Temperatures trend during September in Cook County
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September weather in Cook County day by day
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| 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 | Sunny | 26° /18° | 0.5 mm | 6 | |
| Sept. 17 | Partly cloudy | 25° /18° | 0.5 mm | 6 | |
| Sept. 18 | Cloudy | 24° /17° | 0.8 mm | 5 | |
| Sept. 19 | Patchy rain possible | 24° /17° | 4.4 mm | 5 | |
| Sept. 20 |  Thundery outbreaks possible | 27° /18° | 4 mm | 6 | |
| Sept. 21 | Moderate or heavy rain shower | 24° /18° | 3.6 mm | 6 | |
| Sept. 22 | Patchy rain possible | 22° /16° | 10 mm | 5 | |
| Sept. 23 | Patchy rain possible | 20° /15° | 1 mm | 5 | |
| Sept. 24 |  Overcast | 22° /15° | 2.1 mm | 5 | |
| Sept. 25 | Overcast | 22° /15° | 0.6 mm | 5 | |
| Sept. 26 |  Mist | 23° /14° | 5.1 mm | 6 | |
| Sept. 27 | Sunny | 23° /15° | 1.9 mm | 5 | |
| Sept. 28 | Patchy rain possible | 19° /15° | 0.1 mm | 5 | |
| Sept. 29 | Sunny | 22° /15° | 2.1 mm | 5 | |
| Sept. 30 | Sunny | 22° /16° | 0 mm | 6 | |
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Important Notice
Our weather forecast for Cook County in September is based on the analysis of historical data rather than real-time forecast models. While this provides a general overview, weather conditions can change. We recommend that you check the Cook County forecast closer to your planned date for the most up-to-date weather information.
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Cook County in September - FAQ
What are the expected maximum and minimum temperatures in Cook County during September?
During September, expect a variety of temperatures with highs around 24° and lows near 17°, suitable for diverse activities and preferences.
How much rainfall should be expected in Cook County during September?
Moderate rainfall is anticipated in Cook County during September, with a total of 71.9 mm spread over approximately 13 days. Considering plans for rainy days is advisable.
What are the typical wind conditions in Cook County during September?
The average wind speed in Cook County during September is 19 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Cook County
Explore the daily rainfall trends and prepare for Cook Countys September weather 💧
UV exposure in Cook County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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