Cliffside Park is a borough in Bergen County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 23,594, reflecting an increase of 587 (+2.6%) from the 23,007 counted in the 2000 Census, which had in turn increased by 2,614 (+12.8%) from the 20,393 counted in the 1990 Census.