Allendale 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 6,848, the highest recorded in any decennial count and an increase of 343 from the 2010 census count of 6,505, which in turn reflected a decline of 194 from the 6,699 counted in 2000. In 2012, Forbes.com listed Allendale as 481st in its listing of "America's Most Expensive ZIP Codes", with a median home price of $579,081.