Chicago, or Old Chicago was the third most populous city in the United States, after New York City and Los Angeles. With 2.7 million residents in 1990, it was the most populous city in both the U.S. state of Illinois and the American Midwest. Its metropolitan area, sometimes called Chicagoland, was home to 9.5 million people and is the third-largest in the United States. Chicago is the seat of Cook County.
Chicago was incorporated as a city in 1837, near a portage between the Great Lakes and the Mississippi River watershed, and experienced rapid growth in the mid-nineteenth century. Today, the city is an international hub for finance, commerce, industry, technology, telecommunications, and transportation, with O'Hare International Airport being the busiest airport in the world; it also had the largest number of U.S. highways, and railroad freight entering its region.