Illinois weather in December
December is one of the least pleasant months in Illinois: highs of 3°C (37°F) and about 58 mm (2.3 in) of rain on average. Nights average -2°C (29°F) and cloud cover 73% (NASA POWER, 2001–2025 averages). It is the 3rd driest month of the year and the 3rd coolest. Compared with November, it is cooler and about as wet; January brings highs of 0°C (32°F) and 48 mm (1.9 in) of rain.
Figures are long-term averages for Chicago, the largest city in Illinois. See below for other places.
Is December a good time to visit Illinois?
least pleasant month Weather score 36/100.
December is one of the least pleasant months for weather in Illinois. For better conditions, consider Jun–Sep.
Does it rain a lot in Illinois in December?
No, it is usually dry: about 58 mm (2.3 in) falls in an average December. It is the 3rd driest month of the year.
How warm is Illinois in December?
Days average 3°C (37°F) and nights -2°C (29°F).
Illinois weather by month
| Month | High | Low | Rain | Cloud | Weather |
|---|---|---|---|---|---|
| January | 0°C (32°F) | -5°C (23°F) | 48 mm | 71% | least pleasant |
| February | 0°C (33°F) | -5°C (23°F) | 54 mm | 70% | least pleasant |
| March | 5°C (41°F) | -1°C (31°F) | 62 mm | 66% | least pleasant |
| April | 10°C (50°F) | 4°C (39°F) | 95 mm | 63% | least pleasant |
| May | 15°C (59°F) | 9°C (47°F) | 117 mm | 64% | fair |
| June | 21°C (70°F) | 15°C (59°F) | 102 mm | 56% | best |
| July | 25°C (77°F) | 20°C (68°F) | 95 mm | 48% | best |
| August | 25°C (77°F) | 20°C (68°F) | 105 mm | 48% | best |
| September | 22°C (71°F) | 16°C (62°F) | 86 mm | 46% | best |
| October | 15°C (59°F) | 10°C (49°F) | 99 mm | 58% | fair |
| November | 9°C (47°F) | 4°C (38°F) | 61 mm | 63% | least pleasant |
| December | 3°C (37°F) | -2°C (29°F) | 58 mm | 73% | least pleasant |
Sources: 2001–2025 monthly averages from NASA POWER (MERRA-2 reanalysis). Page updated . How we rate months
Weather across Illinois in December
Weather can differ a lot within Illinois: coasts, hills and mountains each have their own climate.
| Place | High | Low | Rain | Weather |
|---|---|---|---|---|
| Chicago | 3°C (37°F) | -2°C (29°F) | 58 mm | least pleasant |
| Aurora | 1°C (34°F) | -6°C (20°F) | 57 mm | least pleasant |
| Rockford | 0°C (32°F) | -8°C (18°F) | 54 mm | least pleasant |
| Joliet | 2°C (36°F) | -6°C (21°F) | 57 mm | least pleasant |
| Naperville | 1°C (34°F) | -6°C (20°F) | 57 mm | least pleasant |
| Peoria | 3°C (37°F) | -5°C (22°F) | 61 mm | least pleasant |
| North Peoria | 3°C (37°F) | -5°C (22°F) | 61 mm | least pleasant |
| Elgin | 1°C (34°F) | -6°C (20°F) | 57 mm | least pleasant |
| Waukegan | 1°C (33°F) | -7°C (20°F) | 55 mm | least pleasant |
| West Town | 3°C (37°F) | -2°C (29°F) | 58 mm | least pleasant |
| Champaign | 4°C (39°F) | -5°C (24°F) | 70 mm | least pleasant |