Illinois Weather by Month
Illinois, located in the Midwestern United States, experiences a diverse range of weather patterns throughout the year due to its location and varying topography. The state has a humid continental climate, characterized by hot summers, cold winters, and moderate to high levels of humidity. The northern part of Illinois, including Chicago, typically experiences colder winters with more snowfall compared to the southern regions, which have milder winters and longer growing seasons. Summers are generally hot and humid across the state, with temperatures often reaching into the 80s°F to 90s°F (27°C to 32°C). Spring and fall are transitional seasons, bringing moderate temperatures and vibrant changes in foliage, particularly in rural areas. Illinois also experiences a range of weather phenomena, including thunderstorms, tornadoes, and occasionally, winter storms. This varied climate makes Illinois an attractive destination for those who enjoy experiencing all four seasons, whether you’re exploring the bustling city of Chicago, the scenic countryside, or the historic landmarks scattered throughout the state.
Average Temperature and Precipitation by Month
| Month | Avg Temp (°F) | Avg Temp (°C) | Avg Precipitation (inches) |
|---|---|---|---|
| January | 26°F | -3°C | 1.8 |
| February | 30°F | -1°C | 1.8 |
| March | 41°F | 5°C | 2.7 |
| April | 52°F | 11°C | 3.7 |
| May | 63°F | 17°C | 4.5 |
| June | 72°F | 22°C | 4.1 |
| July | 76°F | 24°C | 4.3 |
| August | 75°F | 24°C | 4.2 |
| September | 67°F | 19°C | 3.2 |
| October | 55°F | 13°C | 3.1 |
| November | 43°F | 6°C | 3.2 |
| December | 31°F | -1°C | 2.5 |
Monthly Weather, Clothing, and Landmarks
January
Weather: January is the coldest month in Illinois, with average temperatures ranging from 15°F to 35°F (-9°C to 2°C). Northern Illinois, including Chicago, experiences significant snowfall, icy conditions, and biting winds. The southern part of the state, while slightly warmer, still sees cold temperatures and occasional snow or freezing rain.
Clothing: To stay warm in January, dress in heavy winter clothing, including thermal layers, a down coat, gloves, scarves, and a hat. Waterproof boots with good insulation are necessary for navigating snow and ice. In the northern regions, additional layers such as snow pants or insulated leggings are recommended.
Landmarks: January is a great time to visit the city of Chicago and enjoy indoor attractions like the Art Institute of Chicago, one of the oldest and largest art museums in the United States. For those interested in history, the Abraham Lincoln Presidential Library and Museum in Springfield offers a comprehensive look at the life and legacy of the 16th President. If you’re a winter sports enthusiast, head to Chestnut Mountain Resort in Galena, where you can ski, snowboard, and enjoy the scenic views of the Mississippi River Valley covered in snow.
February
Weather: February in Illinois remains cold, with temperatures ranging from 18°F to 38°F (-8°C to 3°C). Snowfall continues in the northern parts of the state, while southern Illinois may see a mix of snow, sleet, and rain. The days start to lengthen slightly, but the weather remains mostly cold and wintry.
Clothing: Warm layers are essential in February, including a heavy winter coat, thermal clothing, and insulated boots. Gloves, a hat, and a scarf are necessary to protect against the cold winds. Waterproof outerwear is recommended, particularly in regions prone to snow and ice.
Landmarks: February is an excellent time to explore the indoor cultural attractions of Illinois. Visit the Field Museum in Chicago, where you can discover a wide range of exhibits, from ancient Egyptian artifacts to the famous Tyrannosaurus rex named Sue. For a romantic getaway, head to Galena, a historic town known for its well-preserved 19th-century architecture and charming bed-and-breakfasts. The Illinois State Museum in Springfield offers another great indoor experience, showcasing the natural history and cultural heritage of the state.
March
Weather: March marks the beginning of spring in Illinois, with average temperatures ranging from 30°F to 50°F (-1°C to 10°C). The weather is variable, with the possibility of both snow and rain as the state transitions from winter to spring. Southern Illinois begins to see the first signs of blooming flowers and budding trees.
Clothing: Layered clothing is ideal for March, as temperatures can fluctuate throughout the day. A medium-weight jacket, along with a hat and gloves, is recommended for colder mornings and evenings. Waterproof boots are useful for navigating slushy or wet conditions.
Landmarks: March is a perfect time to visit the Shawnee National Forest in southern Illinois, where early spring brings blooming wildflowers and the awakening of the forest’s wildlife. The forest’s Garden of the Gods, with its unique rock formations, is particularly beautiful in the soft light of early spring. In Chicago, the St. Patrick’s Day Parade is a major event, featuring floats, music, and the annual dyeing of the Chicago River green—a unique and festive spectacle that draws large crowds.
April
Weather: April in Illinois brings more consistent spring weather, with temperatures ranging from 40°F to 60°F (4°C to 16°C). Rain showers become more frequent, helping to green the landscape and encourage the growth of flowers and trees. The state’s northern regions may still experience the occasional cool day, while southern areas warm up more quickly.
Clothing: Light layers, including long-sleeved shirts, a medium-weight jacket, and waterproof footwear, are ideal for April. An umbrella or raincoat is recommended for dealing with spring showers, and comfortable walking shoes are useful for exploring outdoor attractions.
Landmarks: April is a wonderful time to visit the Chicago Botanic Garden, where spring flowers are in full bloom and the gardens are lush and vibrant. The warmer weather also makes it an excellent time to explore the Great River Road in western Illinois, where you can enjoy scenic views of the Mississippi River and visit charming river towns like Alton and Grafton. For history enthusiasts, the Cahokia Mounds State Historic Site near St. Louis, Missouri, offers a glimpse into the ancient Mississippian culture, with guided tours and interpretive centers open to the public.
May
Weather: May sees the full arrival of spring in Illinois, with temperatures ranging from 50°F to 70°F (10°C to 21°C). The weather is mild and pleasant, with frequent sunshine and occasional rain showers. Flowers and trees are in full bloom, making the state’s landscapes particularly beautiful during this time.
Clothing: Light, breathable clothing such as t-shirts, light jackets, and comfortable walking shoes are ideal for May. A rain jacket or umbrella may be needed for occasional showers, and sun protection, including sunscreen and a hat, is recommended.
Landmarks: May is an ideal time to visit Starved Rock State Park, located along the Illinois River, where you can hike among stunning sandstone canyons, waterfalls, and lush greenery. The park’s wildflowers are in full bloom, and the warmer weather makes it perfect for exploring the numerous trails. The Illinois Beach State Park on Lake Michigan’s shores offers beautiful sandy beaches, hiking trails, and birdwatching opportunities. Additionally, the annual Tulip Festival in Fulton, Illinois, celebrates the region’s Dutch heritage with vibrant tulip displays, traditional music, and cultural events.
June
Weather: June ushers in summer across Illinois, with temperatures ranging from 60°F to 80°F (16°C to 27°C). The weather is warm, with longer daylight hours and moderate humidity. The state’s landscapes are lush and green, making it an ideal time for outdoor activities and events.
Clothing: Light, breathable clothing such as shorts, t-shirts, and sandals is recommended for June. A hat, sunglasses, and sunscreen are essential for sun protection, and a light jacket may be useful for cooler evenings, especially in northern regions.
Landmarks: June is an excellent time to explore Chicago’s Millennium Park, where you can enjoy outdoor concerts, public art installations like the famous Cloud Gate (The Bean), and lush gardens. For a more adventurous experience, head to the Mississippi Palisades State Park, where you can hike the bluffs overlooking the Mississippi River, offering breathtaking views and opportunities for birdwatching. The Taste of Chicago, held annually in June, is a must-visit for food lovers, offering a wide variety of culinary delights from the city’s top restaurants and food vendors.
July
Weather: July is the hottest month in Illinois, with temperatures ranging from 65°F to 85°F (18°C to 29°C). The weather is hot and humid, with frequent afternoon thunderstorms providing brief relief from the heat. The long days and warm temperatures make it the peak season for outdoor activities and events across the state.
Clothing: Wear light, breathable clothing such as shorts, tank tops, and sandals. Sun protection is crucial, so be sure to use sunscreen, wear sunglasses, and a hat. A light rain jacket or umbrella may be needed for afternoon thunderstorms.
Landmarks: July is ideal for enjoying the beaches along Lake Michigan, particularly in Chicago, where you can relax on North Avenue Beach or explore Navy Pier, which offers family-friendly attractions, boat tours, and stunning views of the Chicago skyline. For a more rural experience, visit the Illinois Amish Country in Arthur, where you can explore the charming countryside, visit Amish shops, and enjoy traditional homemade goods. The Illinois State Fair, held annually in Springfield in August, is another highlight, featuring agricultural exhibits, live music, carnival rides, and a variety of food vendors.
August
Weather: August continues the hot and humid trend in Illinois, with temperatures ranging from 64°F to 84°F (18°C to 29°C). The heat and humidity remain high, with frequent afternoon thunderstorms. The weather is similar to July, making it a great time for late-summer outdoor activities.
Clothing: Light, airy clothing is recommended in August, including shorts, t-shirts, and sandals. Sunscreen, sunglasses, and a hat are necessary for sun protection. A rain jacket or umbrella is useful for the inevitable afternoon showers.
Landmarks: August is a great time to visit the Illinois State Fair in Springfield, where you can enjoy a wide range of activities, including agricultural exhibits, live music, carnival rides, and delicious fair food. For nature lovers, head to the Cache River State Natural Area in southern Illinois, home to unique wetlands, ancient cypress trees, and diverse wildlife. The warm weather also makes it a great time to explore the Shawnee Hills Wine Trail, where you can tour vineyards, taste local wines, and enjoy the scenic views of the rolling hills.
September
Weather: September brings the first hints of fall to Illinois, with temperatures ranging from 55°F to 75°F (13°C to 24°C). The weather remains warm, but the humidity begins to decrease, making the outdoors more comfortable. The state’s landscapes start to show early signs of fall foliage, particularly in the northern regions.
Clothing: Light layers are ideal for September, with t-shirts and shorts for the warmer parts of the day and a light jacket or sweater for cooler mornings and evenings. Comfortable walking shoes are recommended for exploring outdoor areas.
Landmarks: September is the perfect time to visit the Great River Road along the Mississippi River, where you can enjoy scenic drives and explore historic river towns. The early fall colors make this one of the most picturesque times to explore the region. For a cultural experience, visit the Art Institute of Chicago, where you can explore an extensive collection of artworks from around the world. The Morton Arboretum in Lisle offers beautiful fall foliage and hiking trails, making it an ideal spot for a peaceful walk in nature.
October
Weather: October sees a significant drop in temperatures, ranging from 45°F to 65°F (7°C to 18°C). The fall foliage reaches its peak, particularly in the northern and central parts of the state. The weather is typically dry and sunny, making it perfect for outdoor activities and enjoying the vibrant autumn colors.
Clothing: Warmer layers, including sweaters, jackets, and long pants, are necessary for October. A heavier coat may be needed for cold days, especially in the northern regions. Comfortable walking shoes are essential for exploring trails and parks.
Landmarks: October is the perfect time to visit Starved Rock State Park, where the fall foliage creates a stunning landscape of vibrant reds, oranges, and yellows. The park’s trails offer beautiful views of the Illinois River and the surrounding bluffs. For a unique fall experience, visit the town of Galena, where you can explore historic sites, enjoy fall festivals, and take in the picturesque scenery of the rolling hills covered in autumn colors. The Chicago Botanic Garden also hosts special fall events, including a popular pumpkin display and seasonal exhibits.
November
Weather: November in Illinois sees the onset of winter, with temperatures dropping to between 35°F and 50°F (2°C to 10°C). The fall foliage begins to fade, and the state starts to experience more frequent frosts and the possibility of the first snowfall of the season.
Clothing: Warm layers, including sweaters and jackets, are necessary in November. A winter coat, gloves, and a hat may be needed for colder days, particularly in the northern parts of the state. Waterproof footwear is recommended for dealing with wet or frosty conditions.
Landmarks: November is a great time to visit the Abraham Lincoln Presidential Library and Museum in Springfield, where you can explore exhibits dedicated to the life and legacy of one of America’s most revered presidents. For a more festive experience, head to downtown Chicago to see the Magnificent Mile Lights Festival, which kicks off the holiday season with a grand parade, fireworks, and the lighting of the city’s iconic Christmas tree. The Illinois State Museum in Springfield offers another great indoor experience, showcasing the natural history and cultural heritage of the state.
December
Weather: December in Illinois is characterized by cold temperatures and the approach of winter, with averages ranging from 25°F to 40°F (-4°C to 4°C). Snow is possible, particularly in the northern regions, and the state’s landscapes take on a wintry appearance with bare trees and occasional snow cover.
Clothing: Heavy winter clothing, including coats, scarves, gloves, and hats, is necessary for staying warm in December. Waterproof boots are essential for navigating snow and slush. Layering is key to staying comfortable in the fluctuating indoor and outdoor temperatures.
Landmarks: December is the perfect time to experience the holiday season in Illinois. Visit the Christkindlmarket in Chicago, a traditional German Christmas market offering festive holiday goods, food, and drink. The light displays at Lincoln Park Zoo, known as ZooLights, transform the zoo into a winter wonderland, making it a must-visit for families. For a more historical experience, visit the Ulysses S. Grant Home in Galena, where you can learn about the life of the 18th president while enjoying the festive decorations that adorn the historic home during the holiday season.
