Chicago, Illinois weather in September

Averages from 2021–2025 (150 days of record).

Average high: 75°F
Average low: 61°F
Rainy days: ~7 per month
Total precipitation: 3.3 in
Warmest recorded: 94°F
Coldest recorded: 47°F

Expect September days in Chicago, Illinois to top out around 75°F and cool to about 61°F overnight, with roughly 7 days of measurable rain across the month. In recent years September has ranged from 47°F to 94°F.

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Current Chicago, Illinois forecast → · Historical data by Open-Meteo (ERA5).