Allendale is a borough in Bergen County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 6,505, reflecting a decline of 194 (-2.9%) from the 6,699 counted in the 2000 Census, which had in turn increased by 799 (+13.5%) from the 5,900 counted in the 1990 Census.
Allendale was formed on November 8, 1894 from portions of Franklin Township, Hohokus Township and Orvil Township at the height of the Boroughitis phenomenon then sweeping through Bergen County.
Late science-fiction author Richard Matheson was born here on February 20, 1926.