The Paulins Kill is a 41.6-mile (66.9 km) tributary of the Delaware River in northwestern New Jersey in the United States. With a long-term median flow rate of 76 cubic feet of water per second (2.15 m3/s), it is New Jersey's third-largest contributor to the Delaware River, behind the Musconetcong River and Maurice River. The river drains an area of 176.85 square miles (458.0 km2) across portions of Sussex and Warren counties and 11 municipalities. It flows north from its source near Newton, and then turns southwest. The river sits in the Ridge and Valley geophysical province.