Cook County (Chicago)
September
Weather in Cook County for September 2025
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 26.7 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 21.7 °F by the end of September.
Cook County sees moderate rainfall in September, averaging 10 rainy days.
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20
Dry days
10
Rainy days
0
Snow days
24°/17°
Temperatures
19 km/h
Avg max wind
68 %
Avg humidity
Cook County in September average weather
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| Mon. | Tue. | Wed. | Thu. | Fri. | Sat. | Sun. |
|---|---|---|---|---|---|---|
| 1  25° | 2  27° | 3 29° | 4 30° | 5  31° | 6 26° | 7 19° |
| 8  21° | 9  25° | 10 26° | 11  25° | 12 23° | 13 23° | 14 23° |
| 15 27° | 16  26° | 17 21° | 18 21° | 19  22° | 20 28° | 21 27° |
| 22  24° | 23 21° | 24 21° | 25 23° | 26  23° | 27 21° | 28 20° |
| 29 21° | 30 23° |
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Temperatures trend during September in Cook County
See the weather trend as well as the moving average line
September weather day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 | Sunny | 25° /17° | 0 mm | 7 | |
| Sept. 2 | Partly cloudy | 27° /18° | 0 mm | 7 | |
| Sept. 3 | Partly cloudy | 29° /17° | 0 mm | 7 | |
| Sept. 4 | Sunny | 30° /19° | 0 mm | 8 | |
| Sept. 5 | Patchy rain possible | 31° /21° | 0.6 mm | 8 | |
| Sept. 6 | Light rain shower | 26° /18° | 5 mm | 6 | |
| Sept. 7 | Patchy rain possible | 19° /13° | 0.3 mm | 5 | |
| Sept. 8 | Overcast | 21° /14° | 0 mm | 6 | |
| Sept. 9 | Cloudy | 25° /16° | 0 mm | 6 | |
| Sept. 10 | Partly cloudy | 26° /17° | 0 mm | 7 | |
| Sept. 11 | Moderate or heavy rain shower | 25° /18° | 28.6 mm | 6 | |
| Sept. 12 | Cloudy | 23° /17° | 0 mm | 6 | |
| Sept. 13 | Light rain shower | 23° /17° | 0.6 mm | 5 | |
| Sept. 14 | Overcast | 23° /17° | 0 mm | 6 | |
| Sept. 15 | Cloudy | 27° /18° | 0 mm | 6 | |
| Sept. 16 | Thundery outbreaks possible | 26° /18° | 1.2 mm | 6 | |
| Sept. 17 | Light rain shower | 21° /16° | 1.2 mm | 5 | |
| Sept. 18 | Cloudy | 21° /16° | 0 mm | 5 | |
| Sept. 19 | Heavy rain | 22° /16° | 10.1 mm | 5 | |
| Sept. 20 | Thundery outbreaks possible | 28° /18° | 0.1 mm | 6 | |
| Sept. 21 | Overcast | 27° /19° | 0 mm | 7 | |
| Sept. 22 | Fog | 24° /17° | 18 mm | 6 | |
| Sept. 23 | Sunny | 21° /16° | 0 mm | 5 | |
| Sept. 24 | Overcast | 21° /15° | 0 mm | 5 | |
| Sept. 25 | Patchy rain possible | 23° /16° | 0.1 mm | 5 | |
| Sept. 26 | Patchy light rain with thunder | 23° /15° | 12.8 mm | 6 | |
| Sept. 27 | Light rain shower | 21° /16° | 4.7 mm | 5 | |
| Sept. 28 | Patchy rain possible | 20° /17° | 0.1 mm | 5 | |
| Sept. 29 | Mist | 21° /17° | 5.3 mm | 5 | |
| Sept. 30 | Fog | 23° /17° | 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.
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?
Significant rainfall exceeding 127.2 mm is expected in Cook County during September, occurring over more than 10 days. Preparing for wet conditions is recommended in your planning.
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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