September in Waukegan averages a daily high of 23.1°C with nights around 12.5°C. Expect roughly 10.9 wet days totalling 90.7mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Waukegan is May–September.
Based on CHICAGO WAUKEGAN REGIONAL AIRPORT, IL US (7.1km), 1995–2024. 25 years of September data.