Wallpack Ridge (or Walpack Ridge) is a mountain located in the Ridge and Valley Appalachians physiographic province in Sussex County in northwestern New Jersey. Oriented northeast to southwest, Wallpack Ridge spans from Montague Township south of Port Jervis, New York to the Walpack Bend in the Delaware River near Flatbrookville in Walpack Township. It is a narrow ridge ranging between to in width, and its highest elevation reaches above sea level. The 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.