Average Temperatures for Illinois in September





Average temperatures for September at cities throughout Illinois are listed below.

You can jump to a separate table for each region of the state: Chicago Area, Northern Illinois, Central Illinois and Southern Illinois.

The tables give the normal maximum and minimum temperatures based on weather data collected from 1991 to 2020 by the US National Centers for Environmental Information.

Chicago Area

Average September temperatures
High °F Low °F Place High °C Low °C
76 55 Aurora 24 13
75 55 Chicago Botanical Garden 24 13
77 59 Chicago Midway Airport 25 15
76 57 Chicago O'Hare Airport 24 14
76 53 Elgin 24 12
76 55 Joliet 25 13
75 52 Rochelle 24 11

Northern Illinois

Average temperatures in September
High °F Low °F Place High °C Low °C
74 55 Antioch 23 13
75 53 DeKalb 24 12
75 54 Dixon 24 12
74 51 Freeport 24 11
78 54 Moline 26 12
75 54 Rockford 24 12
73 54 Waukegan 23 12

Central Illinois

Normal temperatures for September
High °F Low °F Place High °C Low °C
80 60 Alton 27 15
76 54 Bloomington 25 12
81 57 Cahokia 27 14
79 56 Champaign 26 13
81 57 Charleston 27 14
79 56 Danville 26 13
78 57 Decatur 25 14
78 55 Kankakee 26 13
76 54 Ottawa 25 12
78 56 Peoria 26 14
78 56 Quincy 26 13
80 56 Springfield 27 13

Southern Illinois

Average September temperatures
High °F Low °F Place High °C Low °C
83 57 Belleville 29 14
82 60 Cairo 28 15
81 56 Carbondale 27 13
79 57 Mt Vernon 26 14
Reference

NOAA National Centers for Environmental Information (NCEI). Climate Normals.

Illinois Temperatures
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