Climate of Illinois, USA
Area-weighted average across Illinois. For where people actually live and travel, see the cities below.
Illinois, a subdivision of United States of America, has a strongly continental climate on average. Area-weighted monthly temperatures across the whole territory range from -4.2°C / 24.4°F in January to 24.1°C / 75.4°F in July, with rainfall from 46 mm / 1.8 in to 106 mm / 4.2 in depending on the season (984 mm / 38.7 in total across the year). See the 3 cities listed below for point-value climate at specific locations — these often differ from the area-weighted average, especially in geographically diverse subdivisions.
| Month | Temperature | Rainfall | Matches |
|---|---|---|---|
| January | -4.2°C24.4°F | 46 mm1.8″ | Snowy |
| February | -1.4°C29.5°F | 47 mm1.9″ | Snowy |
| March | 4.7°C40.5°F | 82 mm3.2″ | — |
| April | 10.9°C51.6°F | 97 mm3.8″ | — |
| May | 16.8°C62.2°F | 106 mm4.2″ | — |
| June | 21.9°C71.4°F | 102 mm4″ | — |
| July | 24.1°C75.4°F | 100 mm3.9″ | — |
| August | 22.9°C73.2°F | 92 mm3.6″ | — |
| September | 19°C66.2°F | 89 mm3.5″ | — |
| October | 12.6°C54.7°F | 72 mm2.8″ | — |
| November | 5.4°C41.7°F | 81 mm3.2″ | — |
| December | -1°C30.2°F | 70 mm2.8″ | Snowy |
Frequently asked questions
What is the best time to visit Illinois?
Illinois, United States of America does not have a clear sunny-and-dry window by our cutoffs. The warmest month is July at 24.1°C / 75.4°F, and the driest is January at 46 mm / 1.8 in — likely your best travel window. For city-level detail, see the cities section below.
What is the climate of Illinois?
Illinois, United States of America has area-weighted monthly average temperatures ranging from -4.2°C / 24.4°F in January to 24.1°C / 75.4°F in July. Annual rainfall averages about 984 mm / 38.7 in, with the wettest month being May (106 mm / 4.2 in) and the driest January (46 mm / 1.8 in). Because this is an area average across the whole subdivision, local city values can differ substantially.
What is the hottest month in Illinois?
The hottest month in Illinois is July, with an area-wide average temperature of 24.1°C / 75.4°F.
What is the coldest month in Illinois?
The coldest month in Illinois is January, with an area-wide average temperature of -4.2°C / 24.4°F.
When does it rain most in Illinois?
The wettest month in Illinois is May, averaging about 106 mm / 4.2 in of rainfall. The driest is January with about 46 mm / 1.8 in.