Chicago (i/ʃɪˈkɑːɡoʊ/ or /ʃɪˈkɔːɡoʊ/) is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the third most populous in the U.S.[1] Its metropolitan area, sometimes called "Chicagoland," is the third largest in the United States,[4][5][6] with an estimated 9.8 million people in the U.S. states of Illinois, Wisconsin, and Indiana.[2] Chicago is the county seat of Cook County,[7] the second most populous county in the United States.
Reference: http://en.wikipedia.org/wiki/Chicago,_Illinois