Illinois weather in August 2025

Expect 28°C daytime maximum temperatures in the shade with on average 9 hours of sunshine per day in Illinois in August. Check more long-term weather averages for Illinois in August before you book your next holiday to Illinois in 2025/2026.

  • 28°C maximum daytime temperature in August in Illinois (Chicago)28
    28°C max day temperature
  • 9 hours of sunshine per day
  • 9 days with some rainfall in August in Illinois (Chicago)9
    9 days with some rainfall
  • 16°C minimum night-time temperature in August in Illinois (Chicago)16
    16°C min night temperature
  • 14 hours of daylight per day in August in Illinois (Chicago)14
    14 hours of daylight per day
  • Moderate heat & humidity in August in Illinois (Chicago)M
    Moderate heat & humidity
  • 97 mm monthly rainfall in August in Illinois (Chicago)97
    97 mm of monthly rainfall
  • UV (maximum) index 8 (Very High) in August in Illinois (Chicago)8
    8 (Very High) UV index
  • 21°C sea temperature in August in Illinois (Chicago)21
    21°C sea temperature

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The August 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 August. Select a holiday destination to see more weather parameters.

All Illinois destinations

Metric (°C / mm)  |  Imperial (°F / inches)

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How hot is it in Illinois in August?

Daytime temperatures usually reach 28°C in Chicago, Illinois in August with moderate heat and humidity, falling to 16°C at night.

How sunny is it in Illinois in August?

There are normally 9 hours of bright sunshine each day in Chicago, Illinois in August - that's 67% of daylight hours.

How warm is the sea around Illinois in August?

The average sea temperature around Chicago, Illinois in August is 21°C.

Does it rain in Illinois in August?

There are usually 9 days with some rain in Chicago, Illinois in August and the average monthly rainfall is 97mm.

Illinois August sunrise & sunset times

Browse the sunrise and sunset times for Illinois in August 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
Friday, 1st August 2025 04:45 19:08
Saturday, 16th August 2025 05:00 18:49
Sunday, 31st August 2025 05:16 18:25

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