Chicago is the largest city in Illinois and the third most populous city in the United States. The city has approximately 2.7 million residents. Its metropolitan area, sometimes called 'Chicagoland', is the third-largest in the United States, after New York City and Los Angeles, with an estimated 9.8 million people. Chicago is the county seat of Cook County, though a small portion of the city limits also extend into DuPage County.
Chicago was incorporated as a city in 1837, near a portage between the Great Lakes and the Mississippi River watershed. Today, Chicago is listed as an alpha+ global city by the Globalization and World Cities Research Network, and ranks seventh in the world in the 2012 Global Cities Index. The city is an international hub for finance, commerce, industry, telecommunications, and transportation, with O'Hare International Airport being the second-busiest airport in the world in terms of traffic movements. In 2008, the city hosted 45.6 million domestic and overseas visitors. Among metropolitan areas, Chicago has the fourth-largest gross domestic product (GDP) in the world, just behind Tokyo, the New York City metropolitan area, and Greater Los Angeles, and ahead of London and Paris. Chicago is one of the most important Worldwide Centers of Commerce and trade.
Chicago's notability has found expression in numerous forms of popular culture, including novels, plays, movies, songs, various types of journals (for example, sports, entertainment, business, trade, and academic), and the news media. The city has many nicknames, which reflect the impressions and opinions about historical and contemporary Chicago. The best known include: "Chi-town", "Windy City," "Second City," "Hog Butcher for the World" and the "City of Big Shoulders."