New Hampshire Route 123 (abbreviated NH 123) is a 63.055-mile-long (101.477 km) secondary north–south state highway in southwestern New Hampshire. The southern terminus of the route is at the Massachusetts state line in Mason where, as Mason Road, the road continues as an unnumbered local road in the town of Townsend. The northern terminus, as signed, is at the Vermont border, where NH 123 continues west for a half-mile to U.S. Route 5 as Vermont Route 123. Route logs, however, place the terminus at New Hampshire Route 12 in Walpole.