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Illinois Geography

by Vishul Malik

The US state of Illinois is the fifth-most populous state of the country. It is ranked 25th in size of the 50 states. General Features Illinois is located in the…

The US state of Illinois is the fifth-most populous state of the country. It is ranked 25th in size of the 50 states.

General Features

Illinois is located in the north-central United States. It is bordered by Wisconsin to the north, Iowa and Missouri to the west, Kentucky to the south and Indiana to the east, and the Wabash and Ohio Rivers on the southeast and south.

The landscape of the country can be divided into three major regions : the Central Plains, The Shawnee Hills and the Gulf Coastal Plain.

  • The Central Plains

    Central Plains cover 90% of Illinois. The region stretches from Lake Michigan to the west and south, covering most of the state. This area is further divided into three sections: the Great Lakes Plain, the Driftless Plain and the Till Plain.

  • The Great Lakes Plain:

    It covers the southern half of Michigan, northwest Ohio, northern Indiana, northern Illinois, southern Wisconsin and small area of southwest Minnesota and northwest Iowa. The characteristic topography of the area are glacial moraines and dissected plateaus.

  • The Driftless Plain:

    It covers areas of southern Minnesota and Wisconsin, northwestern Illinois and Northeastern Iowa. It is home to Charles Mound, the highest point in the state. Large hills and valleys are the characteristic topography of this area.

  • The Till Plain:

    The Corn Belt of the state is located in this area. It is mainly cropland (58%), followed by grassland(21%). 19% of the area is wooded. It is the largest section of the Central Plains.

  • The Shawnee Hills

    The Shawnee Hills run across the southern part of Illinois, south of the Central Plains. Rivers, valleys and woodland contribute to the landscape of the region. It is a small strip of land which is characterized by higher elevations. A large area of the Shawnee Hills lies within the Shawnee National Forest, one of the largest protected federal forests in the country.

  • The Gulf Coastal

    The Gulf Coastal stretches from the Gulf of Mexico to the extreme southern tip of Illinois. The area is located between the Ohio River on the east and the Mississippi River on the west. It is sometimes referred to as “Little Egypt” because it resembles the Nile Delta. It is hilly but flattens significantly towards the Kentucky border.

Geographical Facts About Illinois

Area 57,918 square miles
Land Area 55,593 square miles
Water Area 2,325 square miles
Highest point Charles Mound (1,235 feet above sea level)
Lowest point Mississippi River (279 feet above sea level)
Highest temperature 117 degree Fahrenheit
Lowest temperature -36 degree Fahrenheit
Geographic Center Chestnut

Climate of Illinois

Illinois has a widely-varying climate. A significant region of the state has a humid continental climate, with hot, humid summers and cold winters. The southernmost part of the state borders on humid subtropical climate with moderate winters.

Average annual rainfall varies from 1,219 mm in southern tip to around 889 mm in the northern region. Average annual snow varies from 965 mm to 356 mm. The state is vulnerable to tornadoes, with an average of 35 tornadoes occurring annually.


Important rivers of Illinois state are

  • Mississippi River
  • Ohio River
  • Lusk Creek
  • Vermilion River
  • Mazon River
  • Buffalo River


Charles Mound is the highest point in Illinois. Other notable mountains in the state are:

  • Benton Mound (367 m, second-highest mountain in the state)
  • Hudson Mound (356m)
  • Mound Summer (356m)
  • Scales Mound (355m)
  • Horton Hill (297m)
  • Bunker Hill ( 294 m)


Lake Michigan accounts for most of the water present in the state. It is one of the five Great Lakes of North America and is the second-largest of the Great Lakes by volume. Other notable lakes in Illinois are:

  • Anderson Lake
  • Rend Lake
  • Lake Catherine
  • Cedar Lake
  • Grass Lake
  • Grays Lake

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