Old Tappan is a borough in northern Bergen County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 5,888, an increase of 138 from the 2010 census count of 5,750, which in turn reflected an increase of 268 from the 5,482 counted in the 2000 census. Old Tappan was incorporated as a borough by an act of the New Jersey Legislature on October 18, 1894, from portions of Harrington Township, based on the results of a referendum held two days earlier.