After a couple long, sweeping corners through a forest of pine trees, Route 31 enters Paxton.

It passes over a hill past Richards Memorial Library, then uses Grove Street for approximately 1⁄4 mile (0.40 km).

Route 31 then enters Princeton and begins climbing very steeply; it gains about 300 feet (91 m) in approximately 1⁄2 mile (0.80 km).

Entering the center of Princeton, it joins Route 62 and turns east to avoid going over Mount Wachusett.

It passes through a portion of Leominster State Forest in Westminster before an interchange with a freeway segment of Route 2.

The stretch of Route 31 from Paxton Center to Holden Center is named the Chief Robert J. Mortell Memorial Highway, after Paxton chief of police Robert Mortell, who was killed in the line of duty on February 1, 1994, in the deeply wooded area bordering Route 31.