Illinois Climate and Average Weather
Climate of Illinois: average temperatures, rainfall and seasons month by month.
Climate in Illinois month by month
Average high, average low and total rainfall, based on three years of reanalysis data.
| Month | Avg high | Avg low | Rainfall | Rating |
|---|---|---|---|---|
| January | 33° | 19° | 2,4 in | ★★☆☆☆ |
| February | 46° | 27° | 0,8 in | ★★★☆☆ |
| March | 60° | 39° | 3,5 in | ★★★☆☆ |
| April | 67° | 48° | 5,3 in | ★★★☆☆ |
| May | 74° | 56° | 3,9 in | ★★★★☆ |
| June | 83° | 66° | 4,6 in | ★★★★☆ |
| July | 85° | 69° | 5,1 in | ★★★★☆ |
| August | 83° | 67° | 3,0 in | ★★★★☆ |
| September | 82° | 63° | 1,3 in | ★★★★★ |
| October | 69° | 50° | 1,5 in | ★★★★☆ |
| November | 54° | 38° | 3,1 in | ★★★☆☆ |
| December | 43° | 29° | 2,4 in | ★★☆☆☆ |
Climate type: Continental. Source: Open-Meteo archive (ERA5).
Recent extremes in Illinois
Highest and lowest readings observed in the last 3 years of reanalysis data - not all-time records.
How Illinois compares with nearby places
Annual averages, and the difference against Illinois.
| Place | Distance | Avg temp | vs here | Annual rain |
|---|---|---|---|---|
| Gateway Arch National Park | 85 mi | 58°F | +35°F warmer | 46 in |
| St. Louis | 85 mi | 58°F | +35°F warmer | 46 in |
| Missouri | 159 mi | 58°F | +34°F warmer | 40 in |
| Indianapolis | 185 mi | 55°F | 33°F cooler | 45 in |
| Indiana | 185 mi | 55°F | 33°F cooler | 45 in |
Climate by city in Illinois
1 cities mapped in this atlas
Climate by state park in Illinois
1 state and provincial parks mapped in this atlas
Climate by county in Illinois
1 counties mapped in this atlas
Climate by lake in Illinois
1 lakes mapped in this atlas
Best time to visit Illinois
Go in August, September and October. These months score highest on comfortable temperatures, low rainfall and useful daylight.
Hardest months: January, February and December - expect the least comfortable mix of heat, cold or rain.
What this means for Illinois
Today is about average for September. The forecast high of 82°F is in line with the 82°F typical for this month.
A 18% chance means most of the area stays dry; a passing shower is possible but short.
No weather-related travel disruption is expected today. Roads and airports should run normally.
Northern Hemisphere, so peak summer falls in June to August.
The gap between the warmest and coldest month averages 83°F.
What to pack, what to skip
- Lightweight, light-coloured clothing and a refillable water bottle
- Sunglasses, a brimmed hat and SPF 30+
- Layers - the daily swing is 74°F, so mornings feel nothing like afternoons
- A packable rain shell - 2 of the next 7 days carry a real chance of rain
- If your dates are flexible, avoid January, February and December - historically the least comfortable months here.
Summary
Illinois is a state in United States. Illinois is a US state with its capital at Springfield. It has a population of about 12.6 million. The capital is Springfield.
Right now it is 72°F (22°C) in Illinois with overcast. It feels like 74°F. Today runs from 67°F to 82°F. Chance of precipitation is 18%. Sightseeing conditions score 9.3/10 - excellent - go now.
The best time to visit Illinois is August, September and October. The climate is continental. January, February and December tend to be the least comfortable months. July is the warmest month with average highs near 85°F, while January is the coldest with lows near 19°F.
The closest major airport is O'Hare International Airport (ORD), about 177 mi away. Nearby highlights include Starved Rock State Park, Lake Michigan, Gateway Arch National Park and Indiana Dunes National Park.
In plain terms. Today is about average for September. The forecast high of 82°F is in line with the 82°F typical for this month. The best window to be outside is roughly 7 AM to 10 AM, when temperature, rain chance and wind line up best. fishing is the strongest bet in Illinois today at 9.6/10. No weather-related travel disruption is expected today. Roads and airports should run normally.
Compiled from this page's own data: atlas facts plus live Open-Meteo readings.
Quick facts about Illinois
| Type | State |
|---|---|
| Country | United States |
| Continent | North America |
| Coordinates | 39°46′54.1″N 89°39′0.4″W (39.7817, -89.6501) |
| Capital | Springfield |
| Population | 12.600.000 |
| Area | 57.913 sq mi |
| Abbreviation | IL |
| Time zone | America/Chicago |
| Local time | 11:24 PM (UTC-05:00) |
| Best months | August, September and October |
| Climate | Continental |
Weather map for Illinois
Animated model layers. Pick a layer to load it.
Animated layers by Windy. For pin-level detail and nearby places, see the interactive map below.
Explore Illinois
Every topic we hold for this place, and the same topic for the places around it.
Climate for related places
Frequently asked questions
Where is Illinois?
Illinois is a state in United States. Its coordinates are 39.7817, -89.6501. It lies in North America.
What is the weather like in Illinois right now?
It is currently 72°F (22°C) with overcast. Humidity is 68% and wind is 4 mph.
When is the best time to visit Illinois?
August, September and October offer the most comfortable conditions in Illinois, which has a continental climate. January, February and December are usually the hardest months for outdoor plans.
What time zone is Illinois in?
Illinois observes America/Chicago (UTC-05:00). The local time is 11:24 PM.
How many people live in Illinois?
Illinois has a population of approximately 12.6 million.
What is the nearest airport to Illinois?
The closest airports are O'Hare International Airport (ORD), 177 mi away and Nashville International Airport (BNA), 300 mi away.
What are the top things to do in Illinois?
Popular options include Starved Rock State Park, Lake Michigan, Gateway Arch National Park and Indiana Dunes National Park.
What places are in Illinois?
Illinois covers 4 places in this atlas, including Chicago, Starved Rock State Park, Cook County and Lake Michigan.
Related articles
Data sources and methodology
| Place data | USPOTUS Atlas dataset (us-states) - coordinates, hierarchy and facts. |
|---|---|
| Forecast and observations | Open-Meteo (ECMWF and national models). |
| Air quality and pollen | Copernicus CAMS via Open-Meteo. US AQI scale. |
| Climate averages | ERA5 reanalysis via the Open-Meteo archive, aggregated over 3 years. |
| Official alerts | US National Weather Service. |
| Method | Scores, comparisons and advice on this page are computed from the inputs above. Distances are straight-line. Nothing is estimated where data is missing - the block is simply not shown. |
Last updated September 30, 2026 at 11:24 PM local time. Live blocks refresh every 15 minutes; climate averages monthly.
