The route is mostly a two-lane undivided road that passes through rural areas of woodland and farmland.

Route 12 continues southeast through rural areas, crossing the Lockatong Creek before intersecting CR 615, where it becomes the Samuel Hill Highway.

[1] Past this intersection, Route 12 enters Raritan Township, where it continues through rural areas with some residences.

[1][2] Past the traffic circle, the route crosses a small stream and enters Flemington.

[1] Here, Route 12 passes businesses and heads south of a park and ride lot serving Trans-Bridge Lines buses before crossing the Black River and Western Railroad and coming to the Main Street Circle, a modern-designed roundabout, where it intersects CR 611 and Reaville Avenue.

1, approved April 22, 1940, the New Jersey Legislature designated Route 12 from the junction with present-day Route 31 to Croton as the Samuel Hill Highway, in memory of local industrial pioneer Samuel Hill.