The northern terminus of NH 109 is at New Hampshire Route 113 in the village of Center Sandwich in the Lakes Region.

The eastern terminus is at the Maine state line in the town of Wakefield, where the road continues as Maine State Route 109, heading toward the town of Acton.

The northern section of NH 109A is locally named Middle Road.

The southern section is locally named Pine Hill Road.

The southern terminus is in Wolfeboro at New Hampshire Route 28 and NH 109.