New Hampshire Route 25 begins at the state border, on the western bank of the Connecticut River, where it continues west as VT 25. It crosses the river on a metal truss bridge and enters the town of Piermont. Upon reaching Four Corners near the center of Piermont, NH 25 turns north to form a concurrency with NH 10, while the roadway continues east through the intersection as NH 25C, a more direct but rugged route to the town of Warren. Heading north along with NH 10 parallel to the Connecticut River, NH 25 is known locally as Dartmouth College Highway. Upon entering the town of Haverhill, in Haverhill Village, NH 25 leaves the concurrency along Mount Moosilauke Highway, paralleling Oliverian Brook.