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. Arlington Heights is known for the former Arlington Park Race Track, home of the Arlington Million, a Breeders' Cup qualifying event; it also hosted the Breeders' Cup World Thoroughbred Championships in 2002. The village is also home to the Arlington Heights Memorial Library, which has one of the largest collections of books in the state.