What Are the Warmest Cities in Illinois?

What Are the Warmest Cities in Illinois?

The three warmest cities in Illinois are Belleville, Carbondale, and Alton.

In this article I’m going to share with you my ranking of the warmest places in Illinois.

I created my list by researching data provided by the National Oceanic and Atmospheric Administration and other climate data providers.

Below I’m listing the top 10 warmest places in Illinois that have the highest average yearly temperatures. Later in the article I share a table with 50 most populous cities in Illinois.

You may also be interested in my article “Does Chicago Get a Lot of Snow?” For data on sunshine in Chicago, check out my article How Many Sunny Days Does Chicago Get Per Year?

Top 10 Warmest Cities in Illinois

Top 10 Warmest Cities in Illinois

Here are the top 10 warmest places in Illinois ranked by their daily mean temperature. The average annual temperatures in Illinois differ by ten degrees Fahrenheit between the warmest place and the coldest place but only by about 3-4 °F between the top ten cities.

1. Belleville – daily mean temperature of 57.65 °F

Belleville is a city of 42,000 people. Due to its location close to St. Louis, it belongs to the Greater St. Louis metropolitan area. According to weather data collected by NOAA, Belleville is by far the warmest city in Illinois. The average high temperature in the winter in Belleville is 43-49 °F, while nighttime temperatures drop to 24-48 °F. The city gets 7 days of snow a year, with winter precipitation lower than in the summer months. Between June and August Belleville experiences the hottest daytime temperatures in Illinois. They reach 87-90 °F on average, so any potential heat wave may bring unbearably hot weather. Nighttime temperatures drop to 65-68 °F.

2. Carbondale – daily mean temperature of 56 °F

Carbondale is the most southerly located city on this list. With 25,000 residents, it’s the biggest city in Southern Illinois outside of the cities neighboring St. Louis. Compared to Belleville, Carbondale has year round temperatures that are lower by 1-2 degrees. This means cooler winters but also more comfortable summers. Carbondale gets 21 days of rainfall more than Belleville.

3. Alton – daily mean temperature of 55.7 °F

Alton is situated 35 miles northwest of Belleville and lies on the Mississippi River. It has a much more moderate climate than Belleville. In the winter, the average temperature in the coldest month reaches 40 °F (compared to 43 °F in Belleville). In the summer, in the hottest month the average temperature is 87 °F (compared to 90 °F in Belleville).

4. Charleston – daily mean temperature of 55.05 °F

Charleston is a city of 17,000 people. It’s located in Eastern Illinois and forms a metropolitan area with Mattoon, a similarly sized city 12 miles west (though close, they don’t share their average annual temperatures). Charleston has similarly hot summers to Carbondale but it has colder winters, with average highs of 38-43 °F.

5. Mount Vernon – daily mean temperature of 54.5 °F

Mount Vernon is situated 59 miles northeast of Carbondale, still in the southern region of the state. This city of 15,000 people has winter temperatures similar to Charleston, with summers that are cooler at 82-86 °F.

6. Springfield – daily mean temperature of 54.05 °F

The sixth most populous city in Illinois, Springfield, is located in Central Illinois. It sees even cooler winter temperatures, between 36-41 °F, while summers are similar to other cities, with average high temperatures of 84-87 °F. Annual precipitation in Springfield is one of the lowest in this ranking, at 38 inches of rainfall a year. The city gets more days of snowfall, though, at 16 days a year. Springfield enjoys 2,665 sunshine hours a year, with sunny weather conditions even in the coldest months.

7. Quincy – daily mean temperature of 53.75 °F

Quincy, a city of 40,000 people located in Western Illinois on the border with Missouri, has even cooler winters than Springfield, with temperatures between 35-40 °F. It has similar temperatures in the hottest months of June, July, and August.

8. Mattoon – daily mean temperature of 53.6 °F

Mattoon, the city already mentioned along with Charleston, is noticeably cooler than its neighbor. In the winter, it sees average highs of 35-40 °F and lows of 20-25 °F. In Charleston, these temperatures are 38-43 °F and 21-26 °F respectively.

9. Danville – daily mean temperature of 53.1 °F

Danville is a city of 30,000 residents. It’s located in Eastern Illinois, on the border with Indiana, 138 miles south of Chicago. Danville sees temperatures similar to Mattoon, with the only difference notable at night (temperatures are 1-2 degrees lower).

10. Decatur – daily mean temperature of 53 °F

Decatur, a city of 70,000 people, lies 41 miles east of Springfield. It follows the trend of progressively colder winters as we move down the list, seeing average high temperatures of 34-39 °F during the day and 20-25 °F at night. It also has the coolest summers out of all ten cities in this ranking, with highs of 82-85 °F and lows of 63-67 °F. While Decatur is ranked tenth, it’s still much warmer than the coldest places located in Northern Illinois that get average annual temperatures that are up to 5 degrees lower.

50 Biggest Cities in Illinois Ranked by Daily Mean Temperature

Peoria, Illinois

I created the table below by researching data for the most populous municipalities in Illinois. When I couldn’t find data for a given city, I moved on to another. While the list includes 50 cities, some of the bigger cities may be missing because there was no data for them. Please check the closest geographically city then.

CityAverage high temperature (°F)Average low temperature (°F)Daily mean temperature (°F)
Mount Vernon64.244.854.5
Downers Grove624051
Rock Island60.240.550.35
Park Forest59.340.349.8
West Chicago59.240.249.7
New Lenox603949.5
Buffalo Grove5642.649.3
Park Ridge583948.5
Arlington Heights573948
Crystal Lake583848
Vernon Hills58.436.947.65

Check the Warmest Cities in Neighboring States

If you’re interested in learning about the warmest cities in states neighboring Illinois, check out the following articles:

Also check my article on the warmest cities in the US in every state.

Frequently Asked Questions

What is the warmest part of Illinois?

The warmest part of Illinois is its southern part. Some of the warmest cities are located there: Belleville and Alton in the Greater St. Louis metropolitan area and Carbondale further south, north of Shawnee National Forest. Average annual temperatures in these cities are between 56-58 °F. This is 4-5 °F warmer than in the Chicago area.

Does Illinois have harsh winters?

Illinois has cool to mild winters. In Southern Illinois, where the warmest cities are located, temperatures during the day can reach 40-45 °F. In colder parts of the state, such as Northern Illinois by Lake Michigan, temperatures are much colder at 33-38 °F between December and February. In both parts of the state, average low temperatures go well below freezing, dropping to 17-28 °F.

Does Illinois have hot summers?

Illinois has warm to hot summers with average high temperatures reaching up to 90 °F in the warmest parts of the state in Southern Illinois. On average, temperatures are going up to 85 °F. At night, Illinois averages temperatures between 60-65 °F.

Is Illinois colder than New York?

Illinois is warmer than New York by over two degrees. The average temperature for the 50 cities I researched in Illinois is 50.8 °F. Meanwhile, for the 50 cities I researched for New York for the article on the warmest places in New York, the average is 48.4 °F. However, according to weather data collected by NOAA, New York City is warmer than Chicago by over three degrees.

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