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 subdivisons to profit from the coming of the Hackensack and New York Connecting 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 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.
As of the census of 2000, there were 10,087 people, 3,502 households, and 2,850 families residing in the borough. The population density was 3,383.2 people per square mile (1,306.9/km). There were 3,547 housing units at an average density of 1,189.7/sq mi (459.6/km). The racial makeup of the borough was 92.41% White, 0.85% African American, 0.07% Native American, 5.08% Asian, 0.04% Pacific Islander, 0.86% from other races, and 0.69% from two or more races. Hispanic or Latino of any race were 4.25% of the population.
There were 3,502 households out of which 38.1% had children under the age of 18 living with them, 70.8% were married couples living together, 7.7% had a female householder with no husband present, and 18.6% were non-families. 15.7% of all households were made up of individuals and 8.8% had someone living alone who was 65 years of age or older. The average household size was 2.87 and the average family size was 3.20.
In the borough the population was spread out with 26.0% under the age of 18, 5.1% from 18 to 24, 29.0% from 25 to 44, 25.1% from 45 to 64, and 14.8% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 95.0 males. For every 100 females age 18 and over, there were 90.8 males.
The median income for a household in the borough was $82,904, and the median income for a family was $90,861. Males had a median income of $65,052 versus $43,558 for females. The per capita income for the borough was $34,651. About 2.5% of families and 3.3% of the population were below the poverty line, including 2.9% of those under age 18 and 3.0% of those age 65 or over.
Hillsdale is served by New Jersey Transit on the Pascack Valley Line at the Hillsdale train station. The station is located at Broadway and Hillsdale Avenue.
The Pascack Valley Line is a north-south, single-track line with passing sidings providing service to and from Hoboken Terminal with connections via the Secaucus Junction transfer station to New Jersey Transit one-stop service to New York Penn Station and to other NJ Transit rail service. Connections are available at Hoboken Terminal to other New Jersey Transit rail lines, the PATH train, New York Waterways ferry service to the World Financial Center and other destinations and Hudson-Bergen Light Rail service. The line formerly operated only during rush hour but as of October 2007, all day service is available in both directions.
County Route 503 (Kinderkamack Road) passes through Hillsdale. While the Garden State Parkway passes through Hillsdale, there is no interchange on the parkway within the borough. It is accessible via nearby interchange 168. The main east-west road in Hillsdale is Hillsdale Avenue, running nearly the length of the borough. Other main roads in Hillsdale include Pascack Road, Broadway, and Wierimus Road.