Chicago ( /ʃɨˈkɑːɡoʊ/ or /ʃɨˈkɔːɡoʊ/) is the third largest city in the United States, and with more than 2.8 million people, the largest city in the state of Illinois and the Midwestern United States. Located on the southwestern shores of Lake Michigan and next to Indiana, Chicago is the third-most densely populated major city in the U.S., and anchor to the world's 26th largest metropolitan area with over 9.6 million people across three states. The Chicago-Naperville-Joliet MSA also grew more than an estimated 400,000 people between April 1, 2000 and July 1, 2006. Except for the southwest corner of O'Hare International Airport in DuPage County, the city of Chicago is located in Cook County.

Chicago was founded in 1833, near a portage between the Great Lakes and the Mississippi River watershed. The city became a major transportation and telecommunications hub in North America. Today, the city retains its status as a major hub, both for industry and infrastructure, with its O'Hare International Airport as the second busiest airport in the world. In 2007^[update], the city attracted 32.8 million domestic visitors and about 1.15 million foreign visitors.