Chicago is the most populous city in the U.S. state of Illinois and, with over 2.8 million residents, the third-most largest city in the United States . The Chicago metropolitan area (commonly referred to as Chicagoland), located adjacent to Lake Michigan, +show all has a population of more than 9.5 million people living in three U.S. states (Illinois, Wisconsin and Indiana) and was the third largest U.S. metropolitan area in 2000. Chicago is 26th by total population and 686th by population density among the world's largest urban areas and one of the largest cities in North America. The World Cities Study Group at Loughborough University rated Chicago as an alpha world city.

Chicago was founded in 1833, near a portage between the Great Lakes and the Mississippi River watershed, and incorporated as a city in 1837. The city became a major transportation and telecommunications hub. in North America. O'Hare International is the second busiest airport in the world. Chicago is also a major business, financial, and industrial center. The city has a notable and famous political culture, is a stronghold of the Democratic Party, and has been home to numerous influential politicians, including the first African-American President of the United States, Barack Obama.

As of 2007, the city's attractions, business, and commerce bring 44.2 million visitors annually. Making use of its abundant resources, Chicago has a heritage for hosting major local, regional, national, and international events that include entertainment, politics, commerce, culture, and sports. On June 4, 2008, Chicago was chosen as one of the final four city candidates to host the 2016 Summer Olympics and made it to the shortlist as the only American city.

Globally recognized, Chicago has numerous nicknames. These soubriquets reflect the impressions and opinions about historical and contemporary Chicago. The best known of these are: the "Windy City" for the apparent bluster of Chicagoans about their city; "Chi-Town" ; the " Second City" due to second ranking in many areas as well as Chicago's ongoing intention to be number one; and the "City of Broad Shoulders". -show less