 It used to be known as the "Over Kill Neighborhood" or just "Over Kill" — it being over the kill (Hackensack River) from Tappan.Its southern part, known as Eastwood (named in contrast to Westwood), became an independent borough in 1894, but was dissolved and re-absorbed into Washington Township in 1896.River Vale was incorporated as a township in 1906, formed from portions of both Hillsdale and Washington Township.