The Cook County Board of Commissioners is a legislative body made up of 17 commissioners who are elected by district, and a president who is elected county-wide, all for four-year terms. Cook County, which includes the City of Chicago, is the United States' second-largest county with a population of 5.2 million residents. The county board sets policy and laws for the county regarding property, public health services, public safety, and maintenance of county highways. It is presided over by its president and the county's chief executive, currently Toni Preckwinkle.

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.