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 (+2.4%) from the 2010 census count of 5,750, which in turn reflected an increase of 268 (+4.9%) from the 5,482 counted in the 2000 census.

Boroughitis was the creation in the 1890s, usually by referendum, of large numbers of small boroughs in the U.S. state of New Jersey, particularly in Bergen County. Attempts by the New Jersey Legislature to reform local government and school systems led to the breakup of most of Bergen County's townships into small boroughs, which still balkanize the state's political map. This occurred following the development of commuter suburbs in New Jersey, residents of which wanted more government services, whereas the long-time rural population feared the increases in taxation that would result.