New Hampshire Route 123A

New Hampshire Route 123
Map of southern New Hampshire with NH 123 highlighted in red
Route information
Maintained by NHDOT
Length:	63.055 mi (101.477 km)
Major junctions
South end:	Mason Road in Townsend, MA
	NH 31 in Greenville US 202 / NH 101 in Peterborough NH 9 in Stoddard NH 10 in Marlow NH 12 in Walpole
North end:	VT 123 near Walpole
Location
Counties:	Hillsborough, Cheshire, Sullivan
Highway system
New Hampshire Highway System Interstate U.S. State Turnpikes ← NH 122 NH 124 → ← VT 122 VT VT 125 →

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 Connecticut River, where the highway continues west for 0.313 miles (0.504 km) to U.S. Route 5 in Westminster, Vermont, as Vermont Route 123 (VT 123). Route logs, however, place the terminus at New Hampshire Route 12 in Walpole.

In Walpole, NH 123 runs in a wrong-way concurrency with NH 12 north–south alongside the Connecticut River, the water body that represents the border between New Hampshire and Vermont. For the entire length of the NH 12/NH 123 concurrency, NH 123 South is, in reality, heading north on the compass while NH 123 North is traveling to the south.