Arlington Heights is a village in Cook County, Illinois, United States. A northwestern suburb of Chicago, it lies about 25 miles (40 km) northwest of the city's downtown. As of the 2020 census, the village's population was 77,676, making it the 15th-most populous municipality in Illinois.

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.