easeweather.com
Cook County (Chicago)
Akron (OH)Albuquerque (NM)Alexandria (VA)Anaheim (CA)Anchorage (AK)Arlington (VA)Asheville (NC)Atlanta (GA)Atlantic City (NJ)Austin (TX)Baltimore (MD)Baton Rouge (LA)Birmingham (AL)Boston (MA)Bowling Green (KY)Brooklyn (NY)Buffalo (NY)Cape Coral (FL)Charlotte (NC)Chattanooga (TN)Chicago (IL)Cincinnati (OH)Cleveland (OH)Colorado Springs (CO)Columbus (OH)Corpus Christi (TX)Dallas (TX)Dayton (OH)Daytona Beach (FL)Denver (CO)Des Moines (IA)Detroit (MI)El Paso (TX)Fairbanks (AK)Fort Lauderdale (FL)Fort Wayne (IN)Fort Worth (TX)Gatlinburg (TN)Grand Rapids (MI)Harrisburg (PA)Honolulu (HI)Houston (TX)Huntsville (AL)Indianapolis (IN)Jackson (MS)Jacksonville (FL)Juneau (AK)Kansas City (MO)Ketchikan (AK)Key West (FL)Knoxville (TN)Las Vegas (NV)Lexington (KY)Lincoln (NE)Little Rock (AR)Los Angeles (CA)Louisville (KY)Madison (WI)Manhattan (NY)Memphis (TN)Miami (FL)Milwaukee (WI)Minneapolis (MN)Mobile (AL)Montgomery (AL)Nashville (TN)New Orleans (LA)New York City (NY)Newark (NJ)Oklahoma City (OK)Omaha (NE)Orlando (FL)Philadelphia (PA)Phoenix (AZ)Pittsburgh (PA)Portland (OR)Richmond (VA)Sacramento (CA)Salt Lake City (UT)San Antonio (TX)San Diego (CA)San Francisco (CA)San Jose (CA)Savannah (GA)Seattle (WA)Sitka (AK)Skagway (AK)Springfield (MO)St. Louis (MO)St. Petersburg (FL)Tallahassee (FL)Tampa (FL)Toledo (OH)Traverse City (MI)Tulsa (OK)Tyler (TX)Vancouver (WA)Virginia Beach (VA)WashingtonWichita (KS)Winston-Salem (NC) More Locations
United States weather

Weather in Cook County, Illinois for September 2026

Your guide to Cook County weather in September - trends and predictions

    Official Weather Alert ⚠️

  • Flood Advisory - See hour by hour.

    • Temperatures

  • Until now, September 2026 in Cook County has been nearly identical to the historical average, with a temperature of 24.7 °F (showing only a slight deviation of 0.3 °F).

  • The forecast for the next days in Cook County predicts temperatures to be around 19 °F, close to the historical average.

  • In general, the average temperature in Cook County at the beginning of September is 25.6 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 19.7 °F by the end of September.

    • Rain 🌧️

  • Cook County experiences moderate rainfall in September, with an average of 7 rainy days and a total precipitation of 74.3 mm.

    • More

  • New! Chat with our AI weatherman - it’s amazing and free.

Average dry days
23
Dry days
Average rainy days
7
Rainy days
Average snowy days
0
Snow days
Average temperatures
24°/17°
Temperatures
Average wind speed
19 km/h
Avg max wind
Average humidity
66 %
Avg humidity

Cook County Weather September

Move between months or click on a day
August
October
Sun.Mon.Tue.Wed.Thu.Fri.Sat.
1
Sunny
26°
2
Partly cloudy
27°
3
Sunny
27°
4
Moderate rain at times
26°
5
Sunny
26°
6
Sunny
24°
7
Patchy rain possible
23°
8
Sunny
24°
9
Sunny
25°
10
Sunny
25°
11
Cloudy
25°
12
Partly cloudy
23°
13
Overcast
24°
14
Sunny
25°
15
Cloudy
27°
16
Sunny
26°
17
Partly cloudy
25°
18
Cloudy
23°
19
Patchy rain possible
24°
20
Weather Alert Moderate or heavy rain shower
21°
21
Overcast
17°
22
Cloudy
18°
23
Overcast
17°
24
Sunny
20°
25
Patchy rain possible
20°
26
Sunny
22°
27
Sunny
24°
28
Overcast
19°
29
Sunny
14°
30
Overcast
19°

Temperatures trend during September in Cook County

See the weather trend as well as the moving average line

September weather in Cook County day by day

Click on a date for more information
August October
Date Weather Temperatures Rain UV More
Sept. 1 Sunny
Sunny
 26° /18° 0.1 mm 6
Sept. 2 Partly cloudy
Partly cloudy
 27° /19° 0 mm 7
Sept. 3 Sunny
Sunny
 27° /17° 7 mm 6
Sept. 4 Moderate rain at times
Moderate rain at times
 26° /18° 0.4 mm 6
Sept. 5 Sunny
Sunny
 26° /18° 0.2 mm 6
Sept. 6 Sunny
Sunny
 24° /18° 1.9 mm 6
Sept. 7 Patchy rain possible
Patchy rain possible
 23° /16° 2.5 mm 6
Sept. 8 Sunny
Sunny
 24° /16° 0 mm 6
Sept. 9 Sunny
Sunny
 25° /17° 4.4 mm 5
Sept. 10 Sunny
Sunny
 25° /17° 0 mm 6
Sept. 11 Cloudy
Cloudy
 25° /17° 16.9 mm 6
Sept. 12 Partly cloudy
Partly cloudy
 23° /16° 0.1 mm 6
Sept. 13 Overcast
Overcast
 24° /17° 2.2 mm 5
Sept. 14 Sunny
Sunny
 25° /18° 0.5 mm 6
Sept. 15 Cloudy
Cloudy
 27° /18° 1.3 mm 5
Sept. 16 Sunny
Sunny
 26° /18° 1.4 mm 5
Sept. 17 Partly cloudy
Partly cloudy
 25° /18° 6.5 mm 5
Sept. 18 Cloudy
Cloudy
 23° /17° 0.7 mm 5
Sept. 19 Patchy rain possible
Patchy rain possible
 24° /17° 8.1 mm 5
Sept. 20 Moderate or heavy rain shower
Moderate or heavy rain shower
 21° /16° 58.9 mm 1.8
Sept. 21 Overcast
Overcast
 17° /15° 0 mm 2.2
Sept. 22 Cloudy
Cloudy
 18° /13° 0 mm 4.8
Sept. 23 Overcast
Overcast
 17° /14° 0 mm 1.5
Sept. 24 Sunny
Sunny
 20° /14° 0.1 mm 5
Sept. 25 Patchy rain possible
Patchy rain possible
 20° /15° 0.6 mm 5
Sept. 26 Sunny
Sunny
 22° /15° 0 mm 6
Sept. 27 Sunny
Sunny
 24° /16° 0 mm 6
Sept. 28 Overcast
Overcast
 19° /10° 16.7 mm 4
Sept. 29 Sunny
Sunny
 14° /7° 0 mm 4
Sept. 30 Overcast
Overcast
 19° /11° 0.9 mm 5
Next
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.
Change Month
‹
›

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 74.3 mm spread over approximately 7 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 💧
Typically, Cook County has 7 rainy days in September with a total of 74.3 mm of rainfall.

UV exposure in Cook County during September

Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
Top locations in Cook County
Select a location for an accurate weather forecast
Chicago
More Locations

Quick links

More Cook County weather pages
You are here
Location coordinates 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.

Found a mistake?
We appreciate your attention to details. Tell us here.