Arlington Heights is a municipality in Cook County with a small portion in Lake County in the U.S. state of Illinois. A suburb of Chicago, it lies about 25 miles (40 km) northwest of the city's downtown. Per the 2020 Census, the population was 77,676. Per the 2010 Census, it is the most populous community in the United States that is incorporated as a "village", and is the 13th most populous municipality in Illinois, although it is not far ahead of its nearby Illinois neighboring villages of Schaumburg and adjacent Palatine.