Hillsdale is a borough in the New York City metropolitan area in Bergen County, New Jersey, United States.
The populated area today known as Hillsdale took form in the mid-to-late 19th century as land speculators, led by David P. Patterson, developed subdivisions to profit from the coming of the Hackensack and New York Railroad (later New Jersey and New York Railroad). The area was incorporated as Hillsdale Township on March 25, 1898, from portions of Washington Township, which had, in turn, been set off from Harrington Township in 1840. Portions of the township were taken on April 30, 1906, to create the township of River Vale. Hillsdale was reincorporated as a borough by an act of the New Jersey Legislature on March 2, 1923, based on the results of a referendum held on April 24, 1923. The borough's name derives from its location in a "dale among the hills".
According to the United States Census Bureau, the borough had a total area of 2.94 square miles (7.61 km2), including 2.90 square miles (7.52 km2) of land and 0.04 square miles (0.09 km2) of water (1.19%).
A small portion of Woodcliff Lake Reservoir lies inside the borough, at the southeast end of the reservoir, with Church Road following along the southern end of the spillway.
The borough borders Ho-Ho-Kus, Park Ridge, River Vale, Saddle River, Washington Township, Westwood and Woodcliff Lake.
Hillsdale Manor is an unincorporated community located within Hillsdale.
As of the 2010 United States Census, the borough's population was 10,219, reflecting an increase of 132 (+1.3%) from the 10,087 counted in the 2000 Census, which had in turn increased by 337 (+3.5%) from the 9,750 counted in the 1990 Census.
The 2010 United States Census counted 10,219 people, 3,493 households, and 2,843 families in the borough. The population density was 3,464.8 inhabitants per square mile (1,337.8/km2). There were 3,567 housing units at an average density of 1,209.4 per square mile (467.0/km2). The racial makeup was 89.42% (9,138) White, 1.01% (103) Black or African American, 0.12% (12) Native American, 6.26% (640) Asian, 0.05% (5) Pacific Islander, 2.06% (211) from other races, and 1.08% (110) from two or more races. Hispanic or Latino of any race were 7.77% (794) of the population.
Of the 3,493 households, 40.1% had children under the age of 18; 69.6% were married couples living together; 8.5% had a female householder with no husband present and 18.6% were non-families.