Illinois

• 1. Introduction

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  Illinois sits at the geographic and demographic center of the United States, a state that political strategists and journalists have long called a bellwether, captured in the phrase "Will it play in Peoria?" Its 12.8 million residents span the third-largest city in the country and some of the most productive farmland on earth. The northeast corner anchors Chicago on Lake Michigan; the southern tip, a wedge of land where the Mississippi and Ohio Rivers meet, reaches so far south that it shares a climate with the subtropics. How did a single state end up holding two UNESCO World Heritage Sites, leading the nation in nuclear power generation, and sending three sitting presidents to the White House? The answers run from a 15th-century urban civilization near present-day Collinsville all the way to a 793-day budget crisis that stretched into 2018.

• 2. Ancient Cahokia

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  Monks Mound, the centerpiece of the ancient Cahokia site near present-day Collinsville, stands 100 feet high, 951 feet long, and 836 feet wide, covering 13.8 acres and containing roughly 814,000 cubic yards of earth. Its peak, topped by a structure estimated at 105 feet in length, rose 150 feet above the plaza below, making it the largest pre-Columbian structure north of the Valley of Mexico. The civilization that built it constructed more than 100 platform and burial mounds, a 50-acre plaza larger than 35 football fields, and a woodhenge of sacred cedar, all arranged in a planned design that expressed the culture's cosmology.

  Archaeologists have recovered elaborate ceramics, finely sculptured stonework, engraved copper and mica sheets, and a funeral blanket fashioned from 20,000 shell beads at the site. These artifacts point to a true urban center, with clustered housing, markets, and specialists in toolmaking, hide dressing, potting, jewelry making, shell engraving, weaving, and salt making. The Koster Site, excavated nearby, demonstrates 7,000 years of continuous habitation in the Illinois area. The Cahokia civilization vanished in the 15th century for reasons that remain unknown, though historians have speculated that the population depleted the area's resources. Around the time of European contact in 1673, the Illinois Confederation, the next major regional power, had an estimated population of over 10,000 people.

• 3. European Contact and Statehood

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  French explorers Jacques Marquette and Louis Jolliet traveled the Illinois River in 1673. René-Robert Cavelier, Sieur de La Salle and Henri de Tonti built a fort at the site of present-day Peoria in 1680, and another atop Starved Rock in 1682. Illinois passed from French hands to British control in 1763, when France lost the Seven Years' War, but the region saw virtually no British or American colonization because imperial decrees designated it as indigenous lands west of the Appalachians.

  The Illinois Territory was created on the 3rd of February, 1809, with its capital at Kaskaskia. The border question that followed shaped Illinois far more than anyone expected. The original bill submitted to Congress on the 23rd of January, 1818 would have drawn the northern boundary only 10 miles north of Lake Michigan's southern tip, leaving Illinois with almost no usable shoreline. Illinois delegate Nathaniel Pope lobbied for a further push north. The final bill shifted the border to 42 degrees 30 minutes north latitude, roughly 51 miles north of Indiana's border. That single amendment added 8,500 square miles to the state, including the lead mining region near Galena and nearly 50 miles of Lake Michigan shoreline. Pope and others saw the Chicago River as the key to a canal connecting the Great Lakes to the Mississippi. Illinois became the 21st U.S. state in 1818, and the capital moved from Kaskaskia to Vandalia in 1819, then to Springfield in 1837 under a legislative push led by state representative Abraham Lincoln.

• 4. Railroads, Labor, and the Great Migration

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  John Deere's invention of the self-scouring steel plow turned Illinois's rich prairie into some of the world's most productive farmland, drawing immigrant farmers from Germany, Sweden, and elsewhere in the 19th century. The Illinois and Michigan Canal, completed after 1848, and a sprawling railroad network made the state the transportation hub of the nation. Chicago became the world's fastest-growing city by the late 19th century and has been the nation's railroad hub since the 1860s.

  With rapid industrial growth came conflict. The Pullman Strike and the Haymarket Riot, both rooted in Chicago, greatly influenced the development of the American labor movement. From the 8th of October, 1871, through the 10th of October, 1871, the Great Chicago Fire burned through downtown, killing 300 people and destroying four square miles of the city. By 1900, Illinois had a population of nearly 5 million, with white residents comprising 98% of that total. The Great Migration from the South then reshaped the state's demographics, establishing a large Black community particularly in Chicago. By the end of the 20th century, the population had reached 12.4 million. The Chicago metropolitan area now holds about 65% of the state's residents, though the area covers only 9% of the state's land.

• 5. Nuclear Age and Civic Firsts

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  In 1942, the University of Chicago conducted the world's first sustained nuclear chain reaction as part of the Manhattan Project. Argonne National Laboratory, near Chicago, activated the first experimental nuclear power generating system in the United States in 1957. By 1960, Dresden 1, near Morris, became the first privately financed nuclear plant in the country. In 1967, Fermilab, near Batavia, opened a particle accelerator that remained the world's largest for over 40 years. Illinois now leads all states in electricity generated from nuclear power, with eleven plants currently operating.

  Illinois has also been the site of a number of legal and political firsts. In 1847, after lobbying by Dorothea L. Dix, Illinois became one of the first states to establish a system of state-supported treatment of mental illness and disabilities. In 1961, Illinois became the first state to repeal its law against sodomy, following the recommendation of the American Law Institute. It was also the first state to elect a Black person to the U.S. House of Representatives in the post-Reconstruction era, with Oscar De Priest winning election in 1928, and the first to elect a Black woman to the U.S. Senate, with Carol Moseley Braun's victory in 1992. During the Civil War, Illinois ranked fourth among states in soldiers who served in the Union Army, with more than 250,000 men mustered into 150 infantry regiments.

• 6. Economy and Geography Today

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  In 2025, Illinois's gross state product reached $1.201 trillion, placing the state among the 18 largest economies in the world. The state holds headquarters for over 32 Fortune 500 companies and 14 Global 500 companies, including Abbott, Allstate, Archer Daniels Midland, John Deere, Kraft Heinz, McDonald's, United Airlines, and Walgreens. Illinois ranks second in U.S. corn production, with more than 1.5 billion bushels produced annually, and leads the nation in soybean production in most years, harvesting 648.9 million bushels in 2023 alone.

  The state's geography divides into three major sections. Northern Illinois is anchored by Chicago, a city of 2,746,388 residents as of 2020. The Port of Chicago connects to the Atlantic Ocean through the Great Lakes and Saint Lawrence Seaway, which opened in 1959, and to the Gulf of Mexico via the Illinois Waterway. O'Hare International Airport has ranked among the world's busiest airports for decades. Central Illinois, historically prairie and now predominantly agricultural, is known as the Heart of Illinois. Southern Illinois, below U.S. Route 50, includes the region called Little Egypt, named partly after biblical Egypt supplying grain during famine. The highest point in the state is Charles Mound in the Driftless Area of the northwest, standing at 1,235 feet above sea level. The Tri-State Tornado of 1925, one of the deadliest on record, killed 613 people in Illinois alone out of 695 total deaths across three states.

• 7. A Diverse and Evolving Population

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  Illinois is the most racially and ethnically diverse state in the Midwest. As of the 2020 census, 12,812,508 people lived in the state. Non-Hispanic whites make up 58.3% of the population, down from 94.7% in 1970. Hispanic residents, at roughly 18% of the population, are the largest minority group; about 75% of that group is Mexican-American, numbering 1,794,369 people. Illinois is home to the largest population of Mexican descent in the United States outside the Western states.

  The state's Asian-American population has grown from 2.5% in 1990 to over 7% by 2023, with the largest groups being Indian (277,961), Filipino (184,508), and Chinese (160,880). Illinois senator Tammy Duckworth, of Thai descent, is one of only three Asian Americans currently serving in the U.S. Senate. The state's Polish-American population of 761,948 is the highest of any state. Illinois also has the largest concentration of Muslims of any state, at 3.7% of the population, and hosts the largest and oldest surviving Bahai House of Worship in the world, on the shores of Lake Michigan in Wilmette. The first and only American-born Catholic pope, Pope Leo XIV, was born in Chicago and raised in the suburb of Dolton.