Illinois climate
World Climates covers 7 places in Illinois. By annual mean temperature, the warmest is Springfield (12 °C53 °F) and the coolest is Rockford (9 °C48 °F). The wettest is Springfield with 1,001 mm39 in of precipitation per year, the driest Rockford with 967 mm38 in.
The most common climate types (Köppen classification computed from these averages) are hot-summer humid continental (Dfa, 7 places).
The highest monthly average high is in Peoria (30 °C86 °F in July); the lowest monthly average low is in Rockford (−11 °C12 °F in January).
Across the places in Illinois, the months that most often rank as the most comfortable are July, August and September (2, 3 and 7 of 7 places respectively).
Frequently asked questions
Which is the warmest place in Illinois?
By annual mean temperature, the warmest place in Illinois is Springfield at 12 °C53 °F. The coolest is Rockford at 9 °C48 °F.
Where does it rain the most in Illinois?
Springfield gets the most precipitation, 1,001 mm39 in in an average year. The driest place is Rockford with 967 mm38 in.
How many places in Illinois does this site cover?
World Climates has climate data for 7 places in Illinois. Each one has a page with monthly averages for temperature, rainfall, humidity and daylight.
When is the best time to visit Illinois?
It depends on the place. Across Illinois, the months that most often rank as the most comfortable are July, August and September. Check the page of each city for its own best months.
Climate of every place in Illinois
| Place | Year | Max high | Min low | Precip. |
|---|---|---|---|---|
| Chicago | 10 | 25 | −5 | 982 |
| Aurora | 10 | 29 | −10 | 983 |
| Rockford | 9 | 28 | −11 | 967 |
| Joliet | 10 | 29 | −9 | 985 |
| Peoria | 11 | 30 | −8 | 983 |
| Springfield | 12 | 30 | −8 | 1,001 |
| Elgin | 10 | 29 | −10 | 983 |
Year = annual mean temperature; max high = average high of the warmest month; min low = average low of the coldest month; precip. = annual total. Temperatures in °C°F, precipitation in mminches. Sorted by population.
Other cities over 100,000 people
These cities share a NASA POWER grid cell with a larger place, so their averages are shown on that page:
- Naperville → data of Aurora
- North Peoria → data of Peoria
Data: NASA POWER climatology 2001–2025 (MERRA-2 reanalysis, CERES satellite data) — grid-cell averages, not station records. Sources and method.