The city name, recorded variously as Ramopuck, Ramapock, or Ramapough, is of Native American origin, meaning either "sweet water" or "sloping/slanting rocks".
During the American Revolutionary War, Commander-in-Chief George Washington is said to have climbed the Ramapo Torne (near Ramapo hamlet) with a telescope to watch the July 24, 1777 sailing of the British fleet off Sandy Hook in New Jersey.
The Town of Hempstead was formed from part of the Town of Haverstraw in 1791. In 1829 the name was changed to Ramapo.
Ramapo Iron Works, located near present-day Route 17 at the base of Terse Mountain, was a producer of cut nails, wood screws, cotton cloth, and spring steel in the first half of the 19th century. Its founder, Jeremiah H. Pierson, was influential in building the Nyack Turnpike and the New York & Erie Railroad across the county. A cotton mill is still standing on the east side of the road.