Timber Run is a tributary of Rocky Brook in Mercer County, New Jersey in the United States.
Timber Run starts at , in a housing development near Franklin Street (SR-33). It flows south and drains into Quad II Lake, which drains into Rocky Brook at .
Another tributary to Rocky Brook that runs nearby is also called Timber Run. This one starts in the middle of a field between Lake Drive and the original alignment of Milford Rd. It flows west-northwest to a point behind a restaurant located a few hundred feet east of the New Jersey Turnpike. From there, the creek turns west-southwest, and continues until it drains into a narrow recessed section of Peddie Lake. Much of this stream is culverted, and parts of its route are diverted around local businesses and Interchange 8 of the Turnpike.