- Western Terminus:
- River Road (PA 32) in Upper Black Eddy
- Eastern Terminus:
- US 202 and NJ 31 in Flemington
- 11.69 miles
NJ 12 is an east/west route in Hunterdon County, extending from Frenchtown to Flemington. It begins at the Uhlerstown-Frenchtown Bridge, a narrow bridge that crosses the Delaware River to New Jersey from River Road (PA 32) in Upper Black Eddy, Pennsylvania. On the other side of the bridge, NJ 12 follows Bridge Street, Race Street, and Kingwood Avenue through Frenchtown and then runs east to Flemington, where it is known as Parker Avenue. It ends at the northern end of the US 202/NJ 31 multiplex, at the traffic circle where the two routes split. The entire length is a two-lane undivided road.