The highway runs between Franconia in the White Mountains Region to Dalton in the upper Connecticut River valley.

The southern terminus of NH 142 is at the junction with New Hampshire Route 18 in Franconia.

The highway winds north through Bethlehem and Whitefield, then turns northwest to Dalton.

NH 142 runs concurrently with New Hampshire Route 116 for 3.659 miles (5.889 km) in Whitefield.

The northern terminus is in Dalton at New Hampshire Route 135, the Connecticut River Road.