Pennbrook Run is a 2.91 mi (4.68 km) long second-order tributary to Foster Brook.

[2] This is the only stream of this name in the United States.

[1] According to the Geographic Names Information System, it has also been known historically as:[1] Pennbrook Run rises about 0.5 miles southwest of Nichols Run, New York and then flows southwest to meet Foster Brook at Gilmore, Pennsylvania.

Pennbrook Run drains 3.20 square miles (8.3 km2) of area, receives about 45.2 in/year (115 cm/year) of precipitation, and is about 93.93% forested.

[3]