Temperature in Illinois in September

Daytime highs, nighttime lows and the warmest cities in Illinois, the United States of America this September.

Illinois, the United States of America, a region in the United States of America, experiences maximum daytime temperatures in September ranging from 21°C (70°F) in Roscoe to 28°C (82°F) in Metropolis. Nighttime temperatures generally drop to 15°C (59°F) in Metropolis and 9°C (48°F) in Roscoe.

What is the temperature of the different cities in Illinois, the United States of America in September?

Explore the map below to discover average September temperatures at the top destinations in Illinois. For a deeper dive, simply click on any destination dot.

Select a Month

Check the conditions for any month of the year.

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For a detailed overview over the year and the best time to visit Illinois, check out our Illinois's climate page.

See also: Illinois weather by month.

Best Places to Visit in Illinois in September

Click on a destination dot for more details. Toggle the map to compare temperatures or precipitation across Illinois.

Conditions Temperatures Precipitation
Avg daytime high -5°C (23°F) cold → 32°C (90°F) hot

Marker color shows the average daytime high temperature in September: blue is cold, red is hot.

See all September weather averages, cities and regions in Illinois

Illinois temperatures in September: frequently asked questions

How hot does it get in Illinois, the United States of America in September?

Expect daytime temperatures around 24°C (75°F) in Chicago. That makes September a high month for Illinois, the United States of America.

How cold does it get at night in Illinois, the United States of America in September?

Chicago sees nighttime lows close to 14°C (57°F) in September.

What is the warmest city in September in Illinois, the United States of America?

Metropolis tops the warmest city list in our database with average maximum daytime temperatures around 28°C (82°F) and a minimum nighttime temperature of around 15°C (59°F).

What is the coldest city in September in Illinois, the United States of America?

For the month of September, Roscoe is the most temperate city in Illinois, the United States of America based on our records. Highs average 21°C (70°F) and nighttime temperatures dip to around 9°C (48°F).

How much sun does Illinois, the United States of America get in September?

Chicago enjoys approximately 226 hours of sunshine, offering a mostly sunny climate that adds a pleasant and vibrant feel to the month.

Interested in more climate information?

We have much more information about the climate in Illinois.

Weather and climate has detailed information for every country in the world. Are you going to the United States of America? Get detailed historical weather averages for many cities in the United States of America.

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