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 2000, 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 (remainder now Wyckoff), Hohokus Township (remainder now Mahwah) and Orvil Township (remainder now Waldwick). The borough was formed during the "Boroughitis" phenomenon then sweeping through Bergen County, in which 26 boroughs were formed in the county in 1894 alone. The borough was named for Joseph Warner Allen, a surveyor for the Erie Railroad.
Babe Ruth would frequently vacation at the Allendale Hotel, which remains in use as a rooming house.
According to the United States Census Bureau, the borough had a total area of 3.12 square miles (8.08 km2), including 3.10 square miles (8.02 km2) of land and 0.02 square miles (0.05 km2) of water (0.67%).
The borough borders the Bergen County municipalities of Mahwah, Ramsey, Saddle River, Waldwick and Wyckoff.
The 2010 United States Census counted 6,505 people, 2,236 households, and 1,798 families in the borough. The population density was 2,100.7 inhabitants per square mile (811.1/km2). There were 2,388 housing units at an average density of 771.2 per square mile (297.8/km2). The racial makeup was 87.41% (5,686) White, 0.51% (33) Black or African American, 0.05% (3) Native American, 9.64% (627) Asian, 0.00% (0) Pacific Islander, 0.83% (54) from other races, and 1.57% (102) from two or more races. Hispanic or Latino of any race were 4.67% (304) of the population.
Of the 2,236 households, 42.8% had children under the age of 18; 70.8% were married couples living together; 8.1% had a female householder with no husband present and 19.6% were non-families. Of all households, 17.5% were made up of individuals and 10.9% had someone living alone who was 65 years of age or older. The average household size was 2.86 and the average family size was 3.25.
28.4% of the population were under the age of 18, 5.8% from 18 to 24, 18.6% from 25 to 44, 32.7% from 45 to 64, and 14.5% who were 65 years of age or older.