The Cook County Jail, located on 96 acres in South Lawndale, Chicago, Illinois, is operated by the Sheriff of Cook County. It is sometimes referred to as California or Hotel California, as its address is on California Avenue. A city jail has existed on this site since after the Great Chicago Fire of 1871, but major County prisoners were not generally collocated here until closure of the old Hubbard Street Criminal Court Building and jail in 1929. Since then, a 1920s neoclassical and art deco courthouse for the criminal division of the Cook County Circuit Court has operated at the South Lawndale complex.

Cook County is the most populous county in the U.S. state of Illinois and the second-most-populous county in the United States, after Los Angeles County, California. More than 40 percent of all residents of Illinois live within Cook County. As of 2020, the population was 5,275,541. The county seat is Chicago, the most populous city in Illinois and the third most populous city in the United States. The county is at the center of the Chicago metropolitan area.