Weather history and climate summary information is available for the following locations:
- Belleville
- Chicago
- Moline
- Peoria
- Springfield
Warmest May Days
The warmest May days in Illinois are:
| Chicago, Illinois | 2012 | 97°F |
| Chicago, Illinois | 2012 | 97°F |
| Belleville, Illinois | 1953 | 97°F |
| Chicago, Illinois | 1977 | 95°F |
| Moline, Illinois | 2006 | 95°F |
Coldest May Days
The coldest May days in Illinois were:
| Chicago, Illinois | 1966 | 24.1°F |
| Moline, Illinois | 2005 | 25°F |
| Chicago, Illinois | 1983 | 27°F |
| Moline, Illinois | 1975 | 28°F |
| Chicago, Illinois | 1947 | 28.4°F |
Wettest May Days
The wettest single days in May occurred:
| Springfield, Illinois | 1975 | 10.6 inches |
| Chicago, Illinois | 2005 | 10 inches |
| Chicago, Illinois | 1973 | 5.1 inches |
| Peoria, Illinois | 1973 | 5.1 inches |
| Moline, Illinois | 1973 | 4.7 inches |