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Climate in Illinois

Illinois has a varied climate depending on the region. In the northern part of the state, the weather is often cold with hot summers and moderate to heavy winter snowfall. In the southern areas, the climate is more humid and subtropical, with hot, humid summers and mild winters. Overall, Illinois enjoys four distinct seasons that bring everything from beautiful spring flowers to chilly winter snowfalls. Average temperatures range from highs of 90 degrees Fahrenheit in summer to lows of around 20 degrees Fahrenheit in winter. Precipitation also varies widely by region, but generally averages between 35-45 inches per year across the state.

Illinois, Illinois gets 40 inches of rain, on average, per year. The US average is 38 inches of rain per year.

Illinois averages 22 inches of snow per year. The US average is 28 inches of snow per year.

On average, there are 198 sunny days per year in Illinois. The US average is 205 sunny days.

Illinois gets some kind of precipitation, on average, 108 days per year. Precipitation is rain, snow, sleet, or hail that falls to the ground. In order for precipitation to be counted you have to get at least .01 inches on the ground to measure.

Weather Highlights

Summer High: the July high is around 86 degrees
Winter Low: the January low is 17
Rain: averages 40 inches of rain a year
Snow: averages 22 inches of snow a year


Illinois's annual BestPlaces Comfort Index of 7.1 (10=best) indicates it is about average compared to other states in the United States.

8.4 / 5

Summer   /   Winter
September, June and May are the most pleasant months in the state of Illinois, while January and December are the least comfortable months.

Climate Averages
  Illinois, IllinoisUnited States
  39.8 in.38.1 in.
  21.8 in.27.8 in.
  108.2 days106.2 days
  198 days205 days
  604 ft.2443 ft.


Many people confuse weather and climate but they are different. Weather is the conditions of the atmosphere over a short period of time, and climate is how the atmosphere is over long periods of time.

Weather is how the atmosphere is behaving and its effects upon life and human activities. Weather can change from minute-to-minute. Most people think of weather in terms of temperature, humidity, precipitation, cloudiness, brightness, visibility, wind, and atmospheric pressure.

Climate is the description of the long-term pattern of weather in a place. Climate can mean the average weather for a particular region and time period taken over 30 years. Climate is the average of weather over time.

July is the hottest month for Illinois with an average high temperature of 85.6°, which ranks it as about average compared to other states. In Illinois, there are 4 comfortable months with high temperatures in the range of 70-85°. The most pleasant months of the year for Illinois are September, June and May.

Illinois has 20.5 days annually when the high temperature is over 90°, which is about average compared to other states in the U.S.

January has the coldest nighttime temperatures for Illinois with an average of 17.4°. This is colder than most of the U.S. states.

Illinois has 118.3 days annually when the nighttime low temperature falls below freezing, which is about average compared to other states in the U.S.

Illinois averages 6.6 days annually when the nighttime low temperature falls below freezing, which is colder than most states in the U.S.

The humidity is usually comfortable in the state of Illinois but some summer months can be unpleasant. July is the most humid month, though humidity is low for most of the year. The most humid months in the state of Illinois are July, August and June.

May is the wettest month in Illinois with 4.5 inches of rain, and the driest month is January with 2.0 inches. The wettest season is Autumn with 30% of yearly precipitation and 17% occurs in Spring, which is the driest season. Illinois's average annual rainfall of 39.8 inches indicates that it is about average compared to other states in the United States.

May is the rainiest month in Illinois with 11.2 days of rain, and February is the driest month with only 7.4 rainy days. Illinois's annual average of 108.2 days with measurable rain is about average compared to other states in the United States. The rainiest season is Summer when it rains 29% of the time and the driest is Spring with only a 23% chance of a rainy day.

With an average annual snowfall of 21.8 inches, Illinois is less snowy than most states in the United States. January is the snowiest month in Illinois with 6.8 inches of snow, and 5 months of the year have significant snowfall.

  • Annual Rainfall (US Avg: 36.5")
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    Reviews for Illinois    77 Reviews
    Miserable - 11/4/2021
    Dont move to Illinois, I moved here over 11 years ago, I was shocked to find out how rude and whiny people are that live here, the mid west was suppose to be such a good... Read More

    Start Your Review of Illinois

    Just to set the record straight - 9/28/2021
    I just want to say being a resident in Illinois for over 50 years, if you are a fairly hard working person of average intelligence, Illinois is probably one of the best... Read More

    Taxes and fees are killing me - 7/5/2021
    I have lived in illinois my whole life (31years) and the ever increasing taxes and fees are killing me. Rent keeps on going up because of all the tax increases every... Read More

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