Illinois climate by month
January highs across Illinois range from 29°F in Galena to 36°F in Springfield; July highs from 84°F in Joliet to 87°F in Springfield. The most common best months across these cities are April, May, September.
Illinois weather month by month
Average of the 8 Illinois cities on this site, computed from NOAA's unrounded values (so it can differ by a degree from averaging the rounded city figures); individual cities differ, sometimes a lot.
| Month | High | Low | Wet days | Snow |
|---|---|---|---|---|
| January | 32°F | 16°F | 10 | 9.0 in |
| February | 36°F | 20°F | 9 | 7.8 in |
| March | 48°F | 29°F | 10 | 3.8 in |
| April | 61°F | 40°F | 12 | 0.7 in |
| May | 72°F | 51°F | 13 | 0.04 in |
| June | 81°F | 61°F | 11 | 0.0 in |
| July | 85°F | 65°F | 9 | 0.0 in |
| August | 83°F | 63°F | 9 | 0.0 in |
| September | 77°F | 55°F | 8 | 0.0 in |
| October | 64°F | 43°F | 10 | 0.1 in |
| November | 49°F | 32°F | 9 | 1.4 in |
| December | 37°F | 22°F | 10 | 7.0 in |
Regional differences
- Warmest winterSpringfield: January high 36°F
- Coolest summerJoliet: July high 84°F
- Most wet daysChicago: 127 a year
- Fewest wet daysSpringfield: 115 a year
- Most snowChicago: 38.8 in a year
Warmest and coolest Illinois city each month
| Month | Warmest | Coolest | Best month for |
|---|---|---|---|
| January | Springfield 36°F | Galena 29°F | – |
| February | Springfield 41°F | Rockford 33°F | – |
| March | Springfield 53°F | Galena 46°F | – |
| April | Springfield 66°F | Elgin 59°F | 1 city |
| May | Springfield 76°F | Elgin 70°F | 8 cities |
| June | Springfield 84°F | Elgin 80°F | – |
| July | Springfield 87°F | Joliet 84°F | – |
| August | Springfield 85°F | Joliet 82°F | – |
| September | Springfield 80°F | Rockford 75°F | 1 city |
| October | Springfield 67°F | Rockford 62°F | – |
| November | Springfield 53°F | Rockford 47°F | – |
| December | Springfield 41°F | Galena 34°F | – |
By normal daily high. "Best month for": how many of the 8 cities have it among their best months by our comfort score.
Frost and humidity across Illinois
- Earliest typical last frostChicago: Apr 11
- Latest typical last frostElgin: Apr 26
- Most muggy daysSpringfield: 59 a year
- Fewest muggy daysElgin: 32 a year
All Illinois cities
| City | Jan high | Jul high | Wet days/yr | Snow/yr | Best months |
|---|---|---|---|---|---|
| Aurora | 31°F | 84°F | 116 | 27.9 in | May |
| Chicago | 33°F | 85°F | 127 | 38.8 in | May, Sep |
| Elgin | 30°F | 84°F | 124 | 32.1 in | May |
| Galena | 29°F | 85°F | 116 | 37.9 in | May |
| Joliet | 31°F | 84°F | 123 | 16.9 in | May |
| Peoria | 34°F | 86°F | 117 | 26.2 in | May |
| Rockford | 29°F | 84°F | 121 | 37.1 in | May |
| Springfield | 36°F | 87°F | 115 | 21.8 in | Apr, May |
Also covered: Naperville (see Aurora). These cities use the same weather stations as the city named.