Marilla Brook is a 5.66 mi (9.11 km) long third-order tributary to West Branch Tunungwant Creek.

[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] Marilla Brook rises about 6 miles (9.7 km) southwest of Bradford, Pennsylvania, and then flows generally east to meet West Branch Tunungwant Creek about 1-mile southwest of Bradford, Pennsylvania.

Marilla Brook drains 14.41 square miles (37.3 km2) of area, receives about 46.7 in/year (119 cm/year) of precipitation, and is about 86.80% forested.

[3]