Cliffside Park is a borough in Bergen County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 25,693, an increase of 2,099 (+8.9%) from the 2010 census count of 23,594, which in turn reflected an increase of 587 (+2.6%) from the 23,007 counted in the 2000 census.

Bergen County is the most populous county in the U.S. state of New Jersey. As of the 2020 United States census, the county's population was 955,732, its highest decennial count ever and an increase of 50,616 (+5.6%) from the 905,116 recorded at the 2010 census, which in turn reflected an increase of 20,998 (2.4%) from the 884,118 counted in the 2000 census. Located in the northeastern corner of New Jersey and its Gateway Region, Bergen County and its many inner suburbs constitute a highly developed part of the New York City metropolitan area, bordering the Hudson River; the George Washington Bridge, which crosses the Hudson, connects Bergen County with Manhattan. The county is part of the North Jersey region of the state.