Hillsdale is a borough in the northern portion of Bergen County, in the U.S. state of New Jersey, within the New York City metropolitan area. As of the 2020 United States census, the borough's population was 10,143,
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, subject to approval which came in a referendum held on April 24, 1923. The borough's name derives from its location in a "dale among the hills".
Geography
According to the United States Census Bureau, the borough had a total area of 2.94 square miles (7.61 km<sup>2</sup>), including 2.90 square miles (7.52 km<sup>2</sup>) of land and 0.04 square miles (0.09 km<sup>2</sup>) of water (1.19%).
The borough borders Ho-Ho-Kus, Park Ridge, River Vale, Saddle River, Washington Township, Westwood and Woodcliff Lake.
As of 2026, the borough is a member of Local Leaders for Responsible Planning in order to address the borough's Mount Laurel doctrine-based housing obligations.