Weather history and climate summary information is available for the following locations:
- Belleville
- Chicago
- Moline
- Peoria
- Springfield
Warmest September Days
The warmest September days in Illinois are:
| Belleville, Illinois | 1954 | 102.9°F |
| Belleville, Illinois | 1971 | 102.4°F |
| Springfield, Illinois | 2011 | 102°F |
| Belleville, Illinois | 2011 | 100.9°F |
| Springfield, Illinois | 1984 | 100.9°F |
Coldest September Days
The coldest September days in Illinois were:
| Chicago, Illinois | 1984 | 28.9°F |
| Chicago, Illinois | 1974 | 30°F |
| Moline, Illinois | 1984 | 30°F |
| Chicago, Illinois | 1995 | 30°F |
| Moline, Illinois | 2012 | 30°F |
Wettest September Days
The wettest single days in September occurred:
| Moline, Illinois | 2008 | 4.6 inches |
| Springfield, Illinois | 1986 | 4.4 inches |
| Chicago, Illinois | 1977 | 4.1 inches |
| Chicago, Illinois | 2008 | 3.9 inches |
| Peoria, Illinois | 2008 | 3.7 inches |