Geography of Illinois facts for kids

Illinois is a large state located in the central United States. It's surrounded by other states like Wisconsin to the north, Iowa and Missouri to the west, Kentucky to the east and south, and Indiana to the east. Illinois also touches Michigan across Lake Michigan.

Most of Illinois' western border is the mighty Mississippi River. The southeastern and southern borders follow the Wabash River and the Ohio River. Illinois is about 390 miles (630 km) long from north to south and 210 miles (340 km) wide from east to west. Its total area is about 57,918 square miles (149,997 km2).

Quick Facts About Illinois

• Illinois is the 25th largest state in the U.S. by area.
• A big part of its water area, about 2,325 square miles (6,022 km2), comes from Lake Michigan.
• The highest point in Illinois is Charles Mound, located in the northwest, standing at 1,235 feet (376 m) above sea level.
• The lowest point is where the Mississippi River flows past Cairo, Illinois, at 279 feet (85 m) above sea level.
• The average elevation across the state is 600 feet (183 m) above sea level.
• McLean County is the largest county by land area.
• Cook County, which includes Chicago, has the most people and is the largest when you combine land and water.

Illinois' Main Regions

Illinois is divided into three main geographical areas: Northern, Central, and Southern. People in Illinois often call Central and Southern Illinois "downstate Illinois." This term usually means any part of Illinois outside the busy Chicago metropolitan area.

Northern Illinois

Northern Illinois is mostly known for the huge Chicago metropolitan area. This includes the city of Chicago, its many suburbs, and the areas around them where the city is still growing. The "collar counties" are five counties that surround Cook County (where Chicago is). These are DuPage, Kane, Lake, McHenry, and Will counties.

The term "Chicagoland" describes this big metro area. It's a very busy, crowded, and industrial place with people from all over the world. The federal government says the Chicago Metropolitan Area includes 11 counties in Illinois, plus two in Indiana and two in Wisconsin.

Other important areas in Northern Illinois include the Rockford Metropolitan Area in the north-central part of the state, located near Wisconsin on the Rock River. The Quad Cities Metropolitan Area is on both sides of the Mississippi River, shared with Iowa.

In the far northwest, there's a special area called the Driftless Zone. This region wasn't flattened by glaciers, so it has higher, more rugged hills. This is where you'll find Charles Mound, the state's highest point.

Central Illinois

Moving south and west, you'll find Central Illinois. This area is mostly flat prairie land. However, along the Illinois and Mississippi rivers, there are steep hills and bluffs that offer amazing views. The western part of this region was once part of the "Military Tract of 1812" and forms the unique bulge on the state's western side.

Central Illinois is known for its small towns and mid-sized cities. Farming is very important here, especially growing corn and soybeans. Major cities include Peoria and Springfield, which is the state capital. The Champaign-Urbana Metropolitan Area is also in this central region.

Southern Illinois

The third main area is Southern Illinois, which is south of U.S. Route 50. This region is sometimes called "Little Egypt" because it's near where the Mississippi River and Ohio River meet. Southern Illinois has a warmer climate and different crops (like cotton in the past). It also has more rugged, hilly land that wasn't covered by glaciers, and some small oil and coal deposits.

Most people in Southern Illinois live in two main areas:

• The Metro-East area, which is east of St. Louis.
• Cities like Carbondale, Marion, and Herrin.

The Shawnee Hills are a range of hills in Southern Illinois. Most of these hills were not covered by glaciers a long time ago. The flat area along the Mississippi River from Alton to the Kaskaskia River is called the American Bottom. This was where the ancient city of Cahokia was located, and it was also an early French settlement. The first state capital, Kaskaskia, was also here. The very southern tip of Illinois is part of the Gulf Coastal Plain.

Illinois' Geology

Illinois is mostly covered by thick layers of soil, sometimes hundreds of feet deep. Much of this soil is called "Illite" and is very common worldwide. The visible rocks in the state are mostly from the most recent geological period, with older rocks buried deep underground. This rich soil is why Illinois is so good for farming.

Illinois is also a big coal-producing state. Much of the rock underground is from the Pennsylvanian period. These rocks often show "cyclothemes," which are repeating layers of limestone, shale, and coal. It's very rare to find dinosaur bones in Illinois because the Pennsylvanian rocks formed before dinosaurs existed.

Galena, a lead ore, used to be mined in the northwest part of the state. Fluorite, the state mineral, is mined in southeastern Illinois. It's used to make fluorine gas.

You can find cool rocks called Geodes along the Mississippi River in older rock formations. In the far southern parts of the state, there are also Igneous rocks. These formed ages ago when North America almost split apart, and hot rock flowed up into cracks in the Earth.

North of the Illinois River, the bedrock is much older Ordovician sandstone. This sandstone provides ancient sand that's great for making glass and molds for metal casting.

Coal Deposits

Most of Illinois' underground rock belongs to the Pennsylvanian period, especially in the southern part of the state. About 68% of Illinois has layers of coal. Experts estimate there are 211 billion tons of bituminous coal under the surface. This coal has a very high energy value, but it also has a lot of sulfur. This means special equipment is needed to burn it cleanly and reduce air pollution.

Rivers of Illinois

Illinois is largely bordered by rivers, and the Illinois River cuts right through the middle of the state. Some rivers, like the Fox and Rock Rivers, flow into Illinois from Wisconsin. The Iroquois and Kankakee rivers start in Indiana. Other important rivers include the Ohio River, the Kaskaskia River, the Sangamon River, and the Chicago River. The Cache River area in southern Illinois is a special wetland recognized internationally.

Groundwater Supply

Underground water is usually plentiful in Illinois. However, because of ancient glaciers, the gravel deposits underground can be uneven. This sometimes makes it tricky to know how deep the water table is. The Mahomet Aquifer is a very large underground water source that many towns in Central Illinois use for their public water supply.

Plants and Animals

Illinois is home to many different plants and animals. Large mammals you might see include whitetail deer and coyotes. Coyotes are even becoming common in the Chicago area! Other common animals are opossums, raccoons, minks, red and gray foxes, and muskrats. You'll also often see cottontail rabbits and squirrels.

Popular game birds include Canada gooses, mallard ducks, wild turkeys, and bobwhite quails. The northern cardinal is the official state bird. Illinois has about 300 different kinds of birds, and many of them fly through the state on their migration path called the Mississippi Flyway. Efforts to restore wetlands along the Mississippi River and Illinois River are attracting many bird species.

About two-thirds of Illinois was originally covered in prairie grasslands, but much of this land is now used for farming. The southern third of the state is still heavily forested with trees like oak, hickory, and maple.

In the northern part of the state, intense farming has made some animal species rare. However, in the less developed south, animal populations are growing. Large mammals like American bison, gray wolf, American black bear, and elk are generally no longer found living wild in Illinois.

Illinois Climate

Climate types in Illinois.

Illinois has a continental climate. This means it has big temperature changes because there are no mountains or oceans nearby to make the weather milder. The weather is mostly affected by cold air from Canada in the winter and warm, humid air from the Gulf of Mexico in the summer.

High temperatures in the south of the state are usually about 10 to 12°F (5 to 7°C) warmer than in the north. The average yearly temperature is 47°F (8°C) in the north and 58°F (14°C) in the south. Temperatures above 90°F (32°C) happen about 45 days a year in the south and 12 days a year in the north. Temperatures below zero °F (-18°C) happen less than one day a year in the south but about 12 days a year in the north.

Annual rainfall is about 34 inches (86 cm) in the north and 46 inches (117 cm) in the south. Winds usually blow from the west. Average wind speeds are between 8 to 12 mph (13 to 19 km/h) across the state, and they are stronger in winter.

Snowfall averages about 30 inches (76 cm) in the north and 10 inches (25 cm) in the south. However, the amount of snow can change a lot each year. Sometimes, southern Illinois gets very little snow.

Most of Illinois has four clear seasons. The very southern part of the state has many trees that are famous for their beautiful fall colors.

Tornadoes are a common danger, especially in the central part of the state. They happen most often in June and April. Freezing rain is most common in central Illinois.

River Border Changes

The Mississippi River is supposed to be the western border of Illinois. However, in some places, the river has changed its path over time. For example, Kaskaskia, Illinois, which was the first state capital, is now west of the river. A flood destroyed the old town, and the Mississippi River now flows where the lower part of the Kaskaskia River used to be. Also, a small part of Missouri is actually east of the river near Grand Tower, Illinois. Similar changes have happened along the Ohio River border with Kentucky and the Wabash River border with Indiana.