Gilbert Run is a 3.43 mi (5.52 km) long second-order tributary to Marilla Brook.

[2] Gilbert Run rises about 5 miles (8.0 km) northwest of Bradford, Pennsylvania, and then flows south-southeast to meet Marilla Brook about 3 miles west of Bradford, Pennsylvania.

Gilbert Run drains 5.02 square miles (13.0 km2) of area, receives about 46.9 in/year (119 cm/year) of precipitation, and is about 87.51% forested.

[3]