Wallpack Valley (or Walpack Valley) is a valley located in Sussex County in northwestern New Jersey formed by Wallpack Ridge (elevation 600–900 feet) on the west, and Kittatinny Mountain (1400–1800 feet) on the east. Wallpack Ridge separates the Wallpack Valley from the valley of the Delaware River (also known as the Minisink or Minisink Valley), and contains the watershed of the Flat Brook and its main tributaries Big Flat Brook and Little Flat Brook. It is a narrow valley, roughly in length running from Montague Township south of Port Jervis, New York to the Walpack Bend in the Delaware River near Flatbrookville in Walpack Township where the Flat Brook enters the Delaware at 300 feet above sea level.