City of Chicago. Chicago. Chicago ( i/ʃɪˈkɑːɡoʊ/ or /ʃɪˈkɔːɡoʊ/) is the third most populous city in the United States, after New York City and Los Angeles. With 2.7 million residents,[1] it is the most populous city in both the U.S. state of Illinois and the American Midwest. Chicago Symphony Orchestra.