Theater in Chicago describes not only theater performed in Chicago, Illinois, but also to the movement in Chicago that saw a number of small, meagerly funded companies grow to institutions of national and international significance. Chicago had long been a popular destination for touring productions, as well as original productions that transfer to Broadway and other cities. According to Variety editor Gordon Cox, beside New York City, Chicago has one of the most lively theater scenes in the United States. As many as 100 shows could be seen any given night from 200 companies as of 2018, some with national reputations and many in creative "storefront" theaters, demonstrating a vibrant theater scene "from the ground up". According to American Theatre magazine, Chicago's theater is "justly legendary".

Chicago is the most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388 in the 2020 census, it is the third-most populous city in the United States after New York City and Los Angeles. As the seat of Cook County, the second-most populous county in the U.S., Chicago is the center of the Chicago metropolitan area, often colloquially called "Chicagoland" and home to 9.6 million residents.