Illinois is composed of about 60% prairie, 30% hills with prairie, and 10% hills. The prairies cover central, northeastern, eastern, and south central Illinois; hills with prairie are found in northwestern, western, and southern Illinois; hills characterize the Driftless Area of the northwest, the Lincoln Hills in the west-southwest, and the Shawnee Hills in the south—all with relief of less than 305 m (1,000 ft).
Geologically, most of Illinois consists of ancient Precambrian granite overlaid by sedimentary rocks of the Pennsylvanian and Mississippian periods (280-345 million years ago). These formations underlie 80% of the state in a bowl-shaped structure extending from the Shawnee Hills in the south to the Illinois River in the north central. The northern fifth of the state contains bedrock from the Silurian, Ordovician, and Cambrian periods (more than 400 million years ago). After the deposition of bedrock, four glaciers covered 90% of Illinois from 1.2 million to 13,000 years ago. Their effects are seen in glacial deposits, windblown soil (loess), and morainal ridges.
All Illinois soils are cultivable and fall into three soil groups: mollisols—a deep, highly organic, black prairie soil found in the northern two-thirds of the state; alfisols—a shallower, less organic, brown, forest-based soil dominant in the southern third of the state; and alluvium—a mixed, deep, water-deposited soil found in nearly all river valleys.
Each day an average 87 billion l (23 billion gal) of water enter the state’s drainage system. More than 500 streams and rivers and 950 lakes and reservoirs circulate and store the water. The Illinois River is the largest river within the state, draining about 64,750 (25,000). Other large river basins are those of the Kankakee, Sangamon, and Fox. All of the major streams drain into either the Ohio or Mississippi rivers. The Chicago River once flowed eastward into Lake Michigan, but it is now artificially controlled by a series of locks to flow west toward the Des Plaines River. Underground aquifers, found in limestone and sandstone deposits, supply water to many northern cities, although that supply is now low. Surface water provides the rest of the state’s water needs.
The climate of Illinois has distinct north-south fluctuations over the 620-km (385-mi) length of the state. The length, lack of significant elevation, continental location, and dominant westerly frontal pattern influence the climate. Average annual precipitation ranges from 1,130 mm (45 in) in southern Illinois to 880 mm (35 in) in northern Illinois. Heaviest monthly amounts fall during late spring and early summer. Long-term average temperatures also vary from north to south. Winter average temperatures are -4° C (25° F) in the north and 2° C (36° F) in the south. Summer averages are 24° C (75° F) in the north and 26° C (79° F) in the south. Atmospheric storms move across the state from west to east, with convective thunderstorms during spring and summer. Cold- and warm-air frontal systems cause most atmospheric storms in the fall and winter.
The original forest vegetation was initially burned off by early humans, leaving tall prairie grasses, averaging 1.5 to 2 m (5 to 6 ft) in height. Mixed deciduous forests (oak, hickory, maple, beech, sweet gum, elm, ash, cedar, pine, tamarack, fir) covered the southern third of the state and most river valleys. The mixed forest-grass vegetation of the 18th century was cleared quickly by farming. Wildlife includes large numbers of white-tailed deer, rabbit, squirrel, red fox, quail, and pheasant, along with several waterfowl species that fly through seasonally.
Extracted minerals include petroleum, natural gas, clay, silica, fluorspar, lead, zinc, and limestone. Illinois is the fourth-to-sixth largest producer of bituminous coal in the United States, depending on annual fluctuations. The Pennsylvania bedrock that underlies 70% of the state has yielded several billion tons since first mined in 1882. Annual production averages about 60 million tons. Surface water is used for agriculture, industry, city water supplies, and electrical and nuclear power plants.
Although some areas in the state have fewer than one person per square mile, nine metropolitan areas account for about 80% of the population: Chicago, Rockford, Peoria, Springfield, Rock Island-Moline, the Illinois portion of the St. Louis, Mo., metropolitan area, Decatur, Champaign-Urbana-Rantoul, and Bloomington-Normal. Since 1950 these cities have experienced most of the state’s population increase. Growth rates are higher in the many suburban cities in the Chicago area.
Illinois has close ties with its neighboring states. East St. Louis, on the east bank of the Mississippi in the southwestern part of the state, is part of the St. Louis, Mo., metropolitan area. Four bridges connect the two states there. East Chicago, Hammond, and Gary, Ind., are part of the Chicago consolidated statistical area.
In 1900 less than 25% of the entire population of Illinois, but more than 75% of the population of Chicago, was foreign born. By 1990 less than 8% of the state’s population was foreign born. The largest groups were those of Mexican, German, Polish, Irish, and Italian extraction. Most of the foreign born live in the Chicago metropolitan area, which is also the home of the overwhelming majority of the state’s black and Hispanic populations.
The largest Christian denomination in Illinois is the Roman Catholic church. That population, along with a large number of Jews, lives primarily in the Chicago area. Methodist, Lutheran, Baptist, and Presbyterian congregations account for most of the state’s Protestants.
State and local tax revenues began supporting Illinois schools in 1825. The 1970 state constitution continued the state’s responsibility to fund all public schools, and 1985 educational reforms have specified competency levels for every subject at all grade levels in all public schools. Attendance remains mandatory for all children from age 5 to 16.
The University of Illinois was founded at Champaign-Urbana in 1867.
The Chicago Symphony is the state’s largest professional orchestra. Other cultural institutions include the Lyric Opera of Chicago, the Art Institute, the Museum of Science and Industry, the Field Museum of Natural History, the Museum of Contemporary Art, the Newberry Library, and the Du Sable Museum of African-American History, all in Chicago; the Lakeview Museum of Arts and Sciences in Peoria; the Rockford Art Museum; and the State Museum in Springfield. Illinois was also a laboratory for architects Louis Sullivan and Frank Lloyd Wright; some of their designs still stand. The Illinois Arts Council was established to assist the performing and visual arts.
The heritage of Abraham Lincoln in Illinois is preserved at Lincoln’s Monument and Tomb and the Lincoln Home National Historic Site in Springfield. New Salem State Historic Site and the Vandalia Statehouse State Historic Site commemorate the beginnings of territorial settlement. Cahokia Mounds and Dickson Mounds are relics of the state’s Indian past. Other historic sites include the Stephen A. Douglas Monument in Winchester, Kaskaskia Island in the Mississippi River, and the Ulysses S. Grant home in Galena.
The industrial growth of the state was spurred by readily available natural resources, excellent transportation, and skilled laborers. The earliest large industries porcessed agricultural products—meat, grain, and lumber—and manufactured farm implements.
Illinois farmers, with their strong interest in scientific farming, have produced remarkable growth in agricultural productivity in the 20th century. The present Illinois farm is on average about 120 ha (300 acres). The main crops produced include corn, soybeans, wheat, hay, oats, orchard crops, and vegetables. Corn and soybeans are the leading cash commodities. Cattle and hog raising are also significant. The state’s forested land, more than 40% of its area 200 years ago, has been cut back to little more than 10%. Lumbering is a minor industry.
The state’s lakes, reservoirs, and rivers yield millions of kilograms of fish annually. Catches include carp, catfish, largemouth bass, and other species. Dozens of fishing tournaments and other sport-fishing events are held annually in Southern Illinois and on Lake Michigan.
In 1900, Illinois was the third leading manufacturing state, with value added by manufacturing of $570 million. Through the years it has remained among the topranking states in the nation in value added by manufacturing. The state’s leading industries include petroleum refining, nonelectrical machinery, food and food products, electrical equipment, and chemicals. The industrial center of Illinois is Chicago and its many suburbs, with smaller concentrations in Rockford, the Quad Cities (Rock Island, Moline, East Moline, and Davenport, Iowa), Peoria, and the Illinois portion of the St. Louis, Mo., metropolitan area. The Midwest Stock Exchange and Chicago Mercantile Exchange are located in Chicago, as is the Chicago Board of Trade, which has set world agricultural prices since 1848.
Tourists spend more than $6 billion annually—about 7% of the gross state product—in state parks and other recreational facilities. Outdoor recreational facilities are plentiful, and many are accessible throughout the year. Shawnee National Forest, composed of two separate areas, is located in southern Illinois. Major sports stadiums located in Chicago include Soldier Field, Chicago Stadium, Wrigley Field, and Comiskey Park.
Transportation and Trade
Illinois is a major U.S. transportation hub, with interstate highways, one of the nation’s main railroad networks, the busiest airport in the world, and three major inland waterways—the Ohio, Illinois, and Mississippi rivers. The Illinois Waterway provides an access route to the Mississippi River for Great Lakes ships via the Chicago River, Chicago Sanitary and Ship Canal, and Des Plaines and Illinois rivers. Chicago’s O’Hare International Airport serves more than 100,000 passengers daily. The Chicago Port Authority handles millions of metric tons of commerce annually, using both the Navy Pier Port and Lake Calumet Port. Leading exports include metals and metal products, nonelectrical machinery, chemicals, electronic equipment, and transport equipment.
Illinois is one of the leading energy producers and consumers in the United States, with 60% of the state’s power generated by coal-fired thermoelectric plants and 24% from nuclear power. The Illinois Environmental Protection Agency supervises landfills; controls air, soil, stream, and lake pollution; monitors noise levels; checks wastewater treatment plants; and wages court battles against polluters. One experimental project for disposing of treated sludge from the Chicago Sanitary District began in 1974 when barges of sludge were carried on the Illinois River to Fulton County for storage in vacant coal mines in order to bring about, over time, natural chemical reactions for eventual use of the sludge as fertilizer. Although sludge continues to be stored, negative public reaction has inhibited its use on strip-mined land owned by the Chicago District in order to restore it to farmland.
Government and Politics
Illinois was one of the five states created from the Northwest Territory. Six different forms of government operated in Illinois before its first constitution took effect in 1818. That first document was followed by constitutions in 1848, 1870, and 1970. Its 1970 constitution included protection from discrimination for women, protection for a healthy environment, and the right of suffrage for more citizens by relaxing residency requirements. The senate and house of representatives, constituting the state’s general assembly, are selected from 59 districts, each represented by one senator and two at-large representatives. The executive branch includes a team-elected governor and lieutenant governor, assisted by an attorney general, secretary of state, comptroller, and treasurer. The supreme court consists of seven judges elected from five judicial districts for 10-year terms. The appellate court judges, also elected for 10-year terms, serve each of the state’s judicial districts, hearing appeals from state circuit courts, whose judges are elected for 10-year terms.
Local government consists of township, county, and city governments, each electing several officials. Talk of dissolving the township level of government may alter this system. Cities with a population of more than 25,000 and counties with an elected chief executive have home-rule power, including the power to tax.
Illinois’s political parties have at times engaged in questionable practices, but the state’s size has given it an important political role nationally. In the 19th century state officials were mainly Republican, but in the 20th century both political parties have held decision-making power. Also, a clear distinction between a Democratic-voting urban population and a Republican-voting rural or suburban population has emerged.