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[[Illinois]] is in the north-central [[United States]]. Surrounding states are [[Wisconsin]] to the north, [[Iowa]] and [[Missouri]] to the west, [[Kentucky]] to the south, and [[Indiana]] to the east. Illinois also borders [[Michigan]], but only via a water boundary in [[Lake Michigan]]. Nearly the entire western boundary is the [[Mississippi River]], except for a few areas where the river has changed course.

==Statistics==
*Illinois has a maximum north-south distance of {{convert|390|mi}} and {{convert|210|mi}} east-west.
*Total area is {{convert|57918|sqmi|km2}}, ranked 25th in size of the 50 states.
*Water area is {{convert|2325|sqmi|km2}}; [[Lake Michigan]] accounts for most of this.
*[[Charles Mound]] is the highest point in the state at {{convert|1,235|ft}} above sea level.
*The [[Mississippi River]] at [[Cairo, Illinois]] is the lowest point, at {{convert|279|ft}}.
*Average elevation is {{convert|600|ft}} above sea level.
*[[McLean County, Illinois|McLean County]] is the largest county in terms of land area (1,184 sq mi.), while [[Cook County, Illinois|Cook County]] is the largest county in terms of population (5,327,777, as of 2004).

==Geographical divisions==
Illinois has three major geographical divisions: Northern, Central, and Southern. Collectively, central and southern Illinois are often referred to within Illinois as "[[downstate Illinois]]" but with political developments since World War II "Downstate" generally refers to ''all'' of Illinois outside of the Chicago metro area.

===Northern Illinois===
The first is [[Northern Illinois]], dominated by the [[Chicago metropolitan area]], including the city of [[Chicago, Illinois|Chicago]], its suburbs, and the adjoining exurban area into which the metropolis is expanding. The "[[collar counties]]" are the five counties that surround the centrally located Cook County in the Chicago metropolitan area: DuPage County, Kane County, Lake County, McHenry County, and Will County. <ref name="eoc"/>

As defined by the federal government, the Chicago metro area includes a few counties in Indiana and Wisconsin and stretches across much of northeastern Illinois, but not as far as [[Rockford, Illinois|Rockford]], generally along Interstates [[Interstate 80|80]] and [[Interstate 90|90]]. The region is cosmopolitan, densely populated, industrialized, and settled by a wide variety of ethnic groups. The term "[[Chicago metropolitan area|Chicagoland]]" is sometimes used to describe the metro area, including Chicago, its suburbs within Cook County, and the so-called collar counties. The term is said to have been coined by ''[[Chicago Tribune]]'' publisher [[Robert R. McCormick]] <ref name="eoc">{{cite web|url=http://www.encyclopedia.chicagohistory.org/pages/2.html|title=Chicagoland|last=Fuller|first=Jack|date=2005|work=The Electronic Encyclopedia of Chicago |publisher=Chicago Historical Society|accessdate=20 February 2010}}</ref>. The [[Chicagoland Chamber of Commerce]] defines it as all of Cook, and DuPage, Kane, Lake, McHenry and Will counties. <ref>[http://www.chicagolandchamber.org/sub/fast_facts.asp Chicagoland Chamber of Commerce]</ref>
*The [[Quad Cities Metropolitan Area]] is on both sides of the [[Mississippi River]] separating Illinois from [[Iowa]]. The Illinois side includes [[Henry County, Illinois|Henry County]], [[Mercer County, Illinois|Mercer County]], and [[Rock Island County, Illinois|Rock Island County]]. <ref> {{cite web | title = Welcome to the Quad Cities| publisher =City Guide Post Inc.| url =http://www.quadcities.com/| date = | accessdate =2008-02-02 }}</ref>

In extreme northwestern Illinois the [[Driftless Zone]], a region of unglaciated and therefore higher and more [[rugged topography]], occupies a small part of the state. [[Charles Mound]], located in this region, is the state's highest elevation above [[sea level]].

===Central Illinois===
Southward and westward, the second major division is [[Central Illinois]], an area of mostly flat [[prairie]] with the exception of areas along the Illinois and Mississippi rivers that are steeped in hills and bluffs hanging high above the rivers providing commanding views for miles. The western section (west of the Illinois River) was originally part of the [[Military Tract of 1812]] and forms the distinctive western bulge of state. Central Illinois is characterized by small towns and mid-sized cities. Agriculture, particularly [[maize|corn]] and [[soybeans]], figures prominently. Major cities include [[Peoria, Illinois|Peoria]], and [[Springfield, Illinois|Springfield]] (the state capital). The [[Champaign-Urbana Metropolitan Area]] is located in the central region of the state and is composed of ([[Champaign County, Illinois|Champaign]], [[Ford County, Illinois|Ford]], and [[Piatt County, Illinois|Piatt]]) counties, the area had a population of 210,275 at the [[United States Census, 2000|2000 census]]<ref>[http://www.census.gov/population/cen2000/phc-t29/tab03a.pdf Population in Metropolitan and Micropolitan Statistical Areas Ranked by 2000 Population for the United States and Puerto Rico: 1990 and 2000.] U.S. Census Bureau. December 30, 2003. Accessed November 20, 2007.</ref>It is centered at the [[University of Illinois at Urbana-Champaign|University of Illinois]]).

===Southern Illinois===
The third division is [[Southern Illinois]], comprising the area south of [[U.S. Route 50]], and including [[Little Egypt (region)|Little Egypt]], near the juncture of the [[Mississippi River]] and [[Ohio River]]. This region can be distinguished from the other two by its warmer climate, different mix of crops (including [[cotton]] farming in the past), more rugged unglaciated topography, as well as small-scale oil deposits and [[coal]] mining. The population in southern Illinois is concentrated in two areas:
*[[Metro-East]] is an area east of [[St. Louis, Missouri|St. Louis]] and it includes ([[Jersey County, Illinois|Jersey]], [[Madison County, Illinois|Madison]], [[St. Clair County, Illinois|St. Clair]], [[Macoupin County, Illinois|Macoupin]], and parts of [[Bond County, Illinois|Bond]] and [[Calhoun County, Illinois|Calhoun]] from the [[St. Louis Metropolitan Statistical Area]], as well as [[Clinton County, Illinois|Clinton County]].<ref>State of Illinois. [http://lmi.ides.state.il.us/lmr/metroeast.htm Metro-East "Metro East: 1965 to Today", Illinois Labor Market Review] </ref>
*Carbondale, Marion, West Frankfort, Herrin, Murphysboro, Carterville, and the Johnston City area.

The [[Shawnee Hills]] arise in southern Illinois. [[Illinoian (stage)|Illinoian Stage]], about 132,000 to 300,000 years before present, climbed the northern face of the Shawnee Hills, but did not reach the summit. Most of the Shawnee Hills is therefore unglaciated.

The floodplain on the Mississippi River from [[Alton, Illinois|Alton]] to the [[Kaskaskia River]] is the [[American Bottom]], and is the site of the ancient city of [[Cahokia]], and was a region of early French settlement, as well as the site of the first state capital, at [[Kaskaskia, Illinois|Kaskaskia]]. The extreme southern tip of Illinois is in the [[Gulf Coastal Plain]].

==Political geography==
The city of Chicago and some of its older suburbs are heavily [[Democratic Party (United States)|Democratic]]. While this tendency has historically been balanced by [[Republican Party (United States)|Republican]] voters in the suburbs, Democrats have significantly increased their suburban support in the past decade. Central Illinois' largely rural character helps to sustain a largely Republican voting pattern and widespread antipathy toward Chicago. The combination of poorer soil, coal mining and industrialization has caused the southern region to lean Democratic politically, especially in the urbanized region around [[St. Louis, Missouri|Saint Louis]], [[Missouri]].

[[Rockford, Illinois]] is known as a center of liberal [[gypsy moth Republicans|"gypsy moth" Republicans]].

==Geology==
Illinois is mainly covered with soil, hundreds of feet thick in many places. Much of this soil is called, appropriately, "[[Illite]]", and is the most common type of soil on the planet. The visible geology of the State is therefore mainly [[Quaternary]], with rocks buried deeply. The wealth of the State mainly arises from this abundance of soil.

Illinois is a major [[coal]]-producing state. Much of the bedrock surface is of [[Pennsylvanian]] age, including "cyclothemes", regular sequences of limestone, shale and coal layers. Newer rocks may have once existed in the State, but these have been removed by repeated epochs of glaciation. Only tiny areas of newer bedrock exist. The chance of finding dinosaur bones in Illinois is almost nil: the Pennsylvanian rocks were here before the dinosaurs.

[[Galena]], a [[lead]] ore, has been mined in the northwest corner of the State. The ore was processed around [[Peru, Illinois]], where river transport was available to bring the ore to a source of coal. About six tons of coal are needed for each ton of ore.

[[Fluorite]], calcium fluoride, is the State mineral. It is mined in the southeastern portion of the State, around [[Metropolis, Illinois|Metropolis]]. Fluorine gas is produced from fluorite. This is used in the production of [[uranium hexafluoride]] at the [[gaseous diffusion]] plant in [[Paducah, Kentucky]].

[[Geode]]s can be found in the older [[Mississippian]] outcroppings along the [[Mississippi River]].

[[Igneous]] intrusions are found in the far southern areas of the State. Ages ago North America began to split roughly along the lines of the Ohio and Mississippi Rivers. Igneous rock flowed up into fissures, as a new ocean began to form. Had this continued, Illinois might have resembled the [[Arabian Peninsula]], a broken terrain between two continents. This split, however, failed: the continent reclosed, leaving only a few igneous intrusions, and some oil fields, as evidence that it happened.

North of the [[Illinois River]] the bedrock surface is much older [[Ordovician]] sandstone. This sandstone yields ancient sand that is very useful in the production of glass, and in making molds for metal castings.

===Coal===
The majority of Illinois surface [[bedrock]] belongs to the [[Pennsylvanian]] period, particularly the downstate region. About 68% of the state has [[coal]]-bearing strata of this geologic period. According to the Illinois State Geological Survey, 211 billion tons of [[bituminous coal]] are estimated to lie under the surface, having a total heating value greater than the estimated oil deposits in the [[Arabian Peninsula]]. However, this coal has a high [[sulfur]] content and as such requires special equipment to reduce air pollution.

===Rivers===
Illinois is mainly bounded by rivers, and the [[Illinois River]] bisects the state. A few rivers, including the [[Fox River (Illinois)|Fox]] and [[Rock River (Illinois)|Rock]] Rivers enter the State from Wisconsin. The [[Iroquois River|Iroquois]] and [[Kankakee River|Kankakee]] arise in [[Indiana]], but lose their identity before reaching the [[Mississippi River|Mississippi]]. The North Fork of the Vermilion River arises in Indiana, but joins the [[Vermilion River (Wabash River tributary)|Vermilion]], which exits the state before joining the [[Wabash River]] in Indiana.

*[[List of Illinois rivers]]
*[[Watersheds of Illinois]]

===Groundwater===
Subsurface water is generally plentiful in Illinois. However, irregular gravel deposits from glaciation can lead to difficulties predicting depth of the water table.

The [[Mahomet Aquifer]] is a large aquifer used as a source for public water supply by many communities in Central Illinois.

==Flora and fauna==
Large [[mammal]] species currently found in Illinois include [[whitetail deer]] and [[coyote]], with the latter becoming urbanized in the [[Chicago]] area, as well as common in the rural areas. Furbearers commonly found include [[opossum]], [[raccoon]], [[mink]], [[red fox|red]] and [[gray fox]]es, and [[muskrat]]. Commonly seen lagomorphs include the [[cottontail rabbit]] and commonly seen rodents include [[squirrel]]s. Game birds found include [[Canada goose]], [[mallard duck]], [[ruffed grouse]], [[wild turkey]], and [[bobwhite quail]]. The [[cardinal (bird)|cardinal]] is the official state bird. The state has approximately 300 species of birds, many of which migrate on the [[Mississippi Flyway]]. Extensive wetland restoration along the [[Mississippi River]] and [[Illinois River]] are attracting many species.

About two thirds of the state was originally prairie, with much of the area converted to rowcrop farming, while the southern third of the state remains heavily forested with [[oak]], [[hickory]], and [[maple]]. Also, several prairie plants.

Especially in the northern third of the state, intensive agriculture has made some species rare, while population numbers are increasing in the less-developed south. Large mammals [[Extirpation|no longer found]] in Illinois include [[American Bison]], [[Gray Wolf]], [[American Black Bear]], and [[Red Deer|elk]].

==Climate==
{{main|Climate of Illinois}}
Illinois has a [[continental climate]], with large temperature extremes not moderated by either mountains or oceans. Weather is influenced primarily by cold Canadian Arctic air in the winter, and warm, humid air from the [[Gulf of Mexico]] in the summer. High temperatures in the south of the state are about 10 to 12 °F. warmer than the north. Average annual temperature is 47 °F. in the north and 58 °F. in the south. Temperatures greater than 90 °F. occur about 45 days per year in the south, and 12 days per year in the north. Temperatures below zero °F. occur one day or less per year in the south, and 12 days per year in the north. Annual rainfall is {{convert|34|in}} in the north and {{convert|46|in}} in the south.

Prevailing [[winds]] are from the west. Average wind speeds "blowing off the [[prairie]]" are greater in the [[Chicago]] area. Statewide, the wind speeds average {{convert|8|to|12|mph}},and is greater in the winter than in summer.

Snowfall averages {{convert|30|in}} in the north and {{convert|10|in}} in the south, although the actual snowfalls vary greatly by year. In some years, southern Illinois receives very little snowfall, and may never get typical winter weather.

Most of the state has four distinct seasons. The southernmost part of the state is heavily forested and the trees are noted for having beautiful [[Autumn|fall]] colors.

[[Tornado]]es are a common hazard, primarily in the central part of the state, with peak months in June and April. Freezing rain is most common in central Illinois.

==Border anomalies==
The [[Mississippi River]] is the nominal western boundary of the state, except for locations where the river has changed course. [[Kaskaskia, Illinois]], the first state capital, is now west of the river. The Mississippi, due to a flood, destroyed the old town of Kaskaskia, and occupies what was the lower channel of the [[Kaskaskia River]]. A portion of [[Missouri]] is east of the river, near [[Grand Tower, Illinois]]. Similar "avlusions" are found along the [[Ohio River]] border with [[Kentucky]] and the [[Wabash River]] border with [[Indiana]].

== References ==
{{Reflist}}
*Exploring the Land and Rocks of Illinois, Stanley E. Harris, Jr., et al., Southern Illinois University Press, 1977.
*Geology Underfoot in Illinois, Raymond Wiggers, Mountain Press, 1997.

== External links ==
*[http://www.illinois.gov/facts/geography.cfm State of Illinois - Geography facts]
*[http://www.nass.usda.gov/il/1998/9816.htm Illinois climate]
*[http://www.isgs.uiuc.edu/isgshome.html Illinois State Geological Survey]
*[http://dnr.state.il.us/conservation/naturalheritage/florafauna/ Flora and Fauna of Illinois]

{{Illinois}}
{{U.S. political divisions geographies}}

[[Category:Geography of Illinois| ]]

Geography of Illinois - Revision history

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