Illinois weather in August
One place stands in for Illinois here — these are Chicago's numbers, not a statewide average.
Based on 1 weather station, in Chicago. One station — Chicago, where Lake Michigan runs the thermostat; downstate summers come hotter, and the far south of the state sees gentler winters.
Chicago & the Lakefront
Highs near 83°, nights around 65°, and 4.3 in of rain in a typical August.
| Place | Highs / lows | Wet days | The short version |
|---|---|---|---|
| Chicago | 83° / 65° | 7 | Warmest the lake gets all year; swim while it lasts. |
Each place above has its own page for the full story — what the month feels like, what to pack, and whether the timing is right.