Chicago is the most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 census, it is the third-most populous city in the United States after New York City and Los Angeles. As the seat of Cook County, the second-most populous county in the U.S., Chicago is the center of the Chicago metropolitan area, often colloquially called “Chicagoland” and home to 9.6 million residents.

Located on the shore of Lake Michigan, Chicago was incorporated as a city in 1837 near a portage between the Great Lakes and the Mississippi River watershed. It grew rapidly in the mid-19th century. In 1871, the Great Chicago Fire destroyed several square miles and left more than 100,000 homeless, but Chicago’s population continued to grow. Chicago made noted contributions to urban planning and architecture, such as the Chicago School, the development of the City Beautiful movement, and the steel-framed skyscraper.

Chicago is an international hub for finance, culture, commerce, industry, education, technology, telecommunications, and transportation. It has the largest and most diverse finance derivatives market in the world, generating 20% of all volume in commodities and financial futures alone.O’Hare International Airport is routinely ranked among the world’s top six busiest airports by passenger traffic, and the region is also the nation’s railroad hub. The Chicago area has one of the highest gross domestic products (GDP) of any urban region in the world, generating $689 billion in 2018. Chicago’s economy is diverse, with no single industry employing more than 14% of the workforce.