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Illinois weather in September 2025
Expect 24°C daytime maximum temperatures in the shade with on average 8 hours of sunshine per day in Illinois in September. Check more long-term weather averages for Illinois in September before you book your next holiday to Illinois in 2025/2026.
- 2424°C max day temperature
- 8 hours of sunshine per day
- 99 days with some rainfall
- 1212°C min night temperature
- 1212 hours of daylight per day
- 0No heat & humidity
- 8787 mm of monthly rainfall
- 66 (High) UV index
- 1919°C sea temperature
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The September weather guide for Illinois (Chicago) shows long term weather averages processed from data supplied by CRU (University of East Anglia), the Met Office & the Netherlands Meteorological Institute. Find out more about our data sources.
Top Illinois destinations
Below are average maximum temperatures at popular countries, regions and places in Illinois in September. Select a holiday destination to see more weather parameters.
All Illinois destinations
Metric (°C / mm) | Imperial (°F / inches)
More about the USA
How hot is it in Illinois in September?
Daytime temperatures usually reach 24°C in Chicago, Illinois in September, falling to 12°C at night.
How sunny is it in Illinois in September?
There are normally 8 hours of bright sunshine each day in Chicago, Illinois in September - that's 61% of daylight hours.
How warm is the sea around Illinois in September?
The average sea temperature around Chicago, Illinois in September is 19°C.
Does it rain in Illinois in September?
There are usually 9 days with some rain in Chicago, Illinois in September and the average monthly rainfall is 87mm.
Illinois September sunrise & sunset times
Browse the sunrise and sunset times for Illinois in September 2025. Select a month to view Illinois sunrise and sunset times for the next 12 months. The Illinois sunrise and sunset times shown below are for Chicago.
JanFebMarAprMayJunJulAugSepOctNovDec
Date | Sunrise times | Sunset times |
---|---|---|
Monday, 1st September 2025 | 05:17 | 18:23 |
Monday, 15th September 2025 | 05:31 | 17:59 |
Tuesday, 30th September 2025 | 05:47 | 17:33 |
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