Chicago (/ʃɪˈkɑːɡoʊ/ or /ʃɪˈkɔːɡoʊ/, local pronunciation /ʃɪˈkaːɡoʊ/) is the largest city in the U.S. state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous city in the USA, after New York City and Los Angeles. Its metropolitan area, commonly named "Chicagoland," is the 27th most populous urban agglomeration in the world and the third largest in the United States, home to an estimated 9.5 million people spread across the U.S. states of Illinois, Indiana, and Wisconsin. Chicago is the county seat of Cook County, the second largest county in the United States by population after Los Angeles County, California.
Chicago was founded in 1833, near a portage between the Great Lakes and the Mississippi River watershed. Today, the city retains its status as a major hub for industry, telecommunications and infrastructure, with O'Hare International Airport being the second busiest airport, in terms of traffic movements, in the world. In 2008, the city hosted 45.6 million domestic and overseas visitors. As of 2010, Chicago's metropolitan area has the 4th largest Gross Domestic Product (GDP) amongst world metropolitan areas.
The city is a center for business and finance and is listed as one of the world's top ten Global Financial Centers. The World Cities Study Group at Loughborough University rated Chicago as an "alpha world city". In a 2010 survey collaboration between Foreign Policy and A.T Kearney ranking cities, Chicago ranked 6th, just after Paris and Hong Kong. The ranking assesses five dimensions: value of capital markets, diversity of human capital, international information resources, international cultural resources, and political influence. Chicago has been ranked by Forbes as the world's 5th most economically powerful city. Chicago is a stronghold of the Democratic Party and has been home to many influential politicians, including the current President of the United States, Barack Obama.
The city's notoriety expressed in popular culture is found in novels, plays, movies, songs, various types of journals (for example, sports, entertainment, business, trade, and academic), and the news media. Chicago has numerous nicknames, which reflect the impressions and opinions about historical and contemporary Chicago. The best known include: "Chi-town," "Windy City," "Second City," and the "City of Big Shoulders." Chicago has also been called "the most American of big cities."