DuPage County is a county in the U.S. state of Illinois, and one of the collar counties of the Chicago metropolitan area. As of the 2020 census, the population was 932,877, making it Illinois' second-most populous county. Its county seat is Wheaton.

The Chicago metropolitan area, also referred to as the Greater Chicago Area and Chicagoland, is the largest metropolitan statistical area in the U.S. state of Illinois, containing the City of Chicago along with its surrounding suburbs and satellite cities. Encompassing 10,286 square mi (28,120 km2), the metropolitan area includes the city of Chicago, its suburbs and hinterland, that span 14 counties across northeast Illinois, northwest Indiana, and southeast Wisconsin. The MSA had a 2020 census population of 9,618,502 and the combined statistical area which spans up to 19 counties had a population of nearly 10 million people. The Chicago area is the third largest metropolitan area in the United States and the fourth largest metropolitan area in North America and the largest within the Midwest, and the largest in the Great Lakes megalopolis. Its urban area is one of the forty largest in the world.