The North Fork begins at the outlet of Ethan Pond in the southeastern corner of Bethlehem, New Hampshire and just north of the northeastern corner of the Pemigewasset Wilderness in the heart of the White Mountains. The river flows west and enters the town limits of Lincoln, the second-largest town by area in New Hampshire. Passing under the Appalachian Trail (and entering the Pemigewasset Wilderness), the North Fork drops over Thoreau Falls and encounters Whitewall Brook flowing south out of Zealand Notch. Turning southwest, the North Fork flows through a deep valley with Mount Bond to the west, and joins the East Branch of the Pemigewasset in a broad valley directly north of Mount Hancock.