ILIllinois Geography

Geography overview

Illinois occupies the 25th largest area among US states. Located in the Midwest region, specifically the midwest rust subregion, its physical geography reflects its position on the North American continent. It has coastline on the great_lakes.

Geographers typically think about a state's geography in five dimensions: location (where it is relative to other places), place (the physical and human characteristics), region (how it groups with others), movement (the flow of people, goods, and ideas), and human-environment interaction (how people have shaped and been shaped by the environment). This page touches on all five.

Topography and landforms

• Crossed by the Mississippi River

Topography refers to the physical features of the land — mountains, valleys, plains, plateaus, basins. Illinois's topography was shaped over millions of years by tectonic activity, glaciation, erosion, river systems, and (in some regions) volcanic activity. Understanding the topography helps explain everything from where cities developed historically (typically near reliable water sources and navigable rivers) to modern climate patterns (mountains create rain shadows, for instance).

Rivers and waterways

The mighty Mississippi River borders or flows through Illinois. At 2,340 miles, the Mississippi is the second-longest river in the United States (after the Missouri) and historically the principal trade route of the early Republic. The river drains 31 US states and 2 Canadian provinces. The state borders one or more of the Great Lakes — Superior, Michigan, Huron, Erie, or Ontario — which together form the largest freshwater system in the world.

Mountains, elevation, and relief

Illinois has moderate elevation across most of its territory, without dominating mountain ranges. The terrain is more gently rolling or plain-like than dramatically mountainous.

Climate and time zone

Illinois observes Central Time. Winters bring heavy snowfall, especially near the Great Lakes or in mountainous areas.

National parks and protected areas

The National Park Service manages many sites in Illinois — national parks, national monuments, national forests, national wildlife refuges, and historic sites. Outdoor recreation drives significant visitor activity — hiking, camping, hunting, fishing, and wildlife viewing.

Wildlife and biodiversity

Illinois's wildlife reflects its geography. Forests, plains, rivers, and (where applicable) coasts support a wide range of mammals, birds, fish, reptiles, and amphibians. Protected populations of native species are maintained through state and federal wildlife management agencies. State parks and refuges protect critical habitats; hunting and fishing license fees fund much of the wildlife conservation work.

Climate zones within the state

Even within Illinois's moderate area, microclimates vary by elevation and terrain. Coastal regions (where applicable) typically have milder, more humid climates than interior areas. Mountain regions are colder and snowier. Desert regions are hot and dry.

Geology — what made Illinois the way it is

Illinois's present-day geography is the result of geological processes operating over hundreds of millions of years: plate tectonics, volcanic activity, glaciation, erosion, sedimentation. Most of the state's bedrock is sedimentary (limestone, sandstone, shale) or metamorphic (where heat and pressure transformed older rocks), with igneous rocks (granite, basalt) more common in mountainous areas. The last Ice Age (which ended approximately 11,000 years ago) reshaped much of the northern US and shaped lake basins, river valleys, and soil distribution.

Illinois notable firsts

• Birthplace of one or more US presidents

Illinois vs similar states

How does Illinois compare with 3 other states in the same region and size category?

State	Capital	Pop	Area rank	Admitted
Illinois	Springfield	over 10 million	#25	1818
Indiana	Indianapolis	5 to 10 million	#38	1816
Iowa	Des Moines	1 to 5 million	#26	1846
Kansas	Topeka	1 to 5 million	#15	1861

Bordering states (5)

Illinois shares borders with 5 other US states, listed alphabetically below. Each link goes to the dedicated state page.

Similar states to Illinois

If this page interested you, you may also want to explore states with similar geography, history, or culture. These states share Illinois's region (Midwest) and similar size category:

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