NY 331 officially begins at the intersection of Kennedy and Crum Creek (CR 57) roads in the Montgomery County town of St.

[3] The route heads northeast as a narrow, two-lane road through a rural, open area[4] as a county-maintained highway, overlapping with the unsigned CR 57 for 0.17 miles (0.27 km) until the Montgomery–Fulton county line.

Past the county line, the route widens slightly as it traverses rolling hills in a rural part of the town of Oppenheim.

NY 331 soon reaches the small hamlet of Crum Creek, where it connects to the eastern terminus of CR 108.

[4] Past Crum Creek, the route continues on a generally northeastward track through the town, running across numerous, mostly undeveloped hills to reach a junction with the east end of CR 150.