The Calumet River is a system of heavily industrialized rivers and canals in the region between the south side of Chicago, Illinois, and the city of Gary, Indiana. Historically, the Little Calumet River and the Grand Calumet River were one, the former flowing west from Indiana into Illinois, then turning back east to its mouth at Lake Michigan at Marquette Park in Gary. Now the system is part of the Chicago Area Waterway System and through the use of locks flows away from Lake Michigan to the Cal-Sag Channel.

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.