Willow Brook is a tributary of Utley Brook in Susquehanna County and Wyoming County, in Pennsylvania, in the United States. It is approximately 3.7 miles (6.0 km) long and flows through Lenox Township in Susquehanna County and Nicholson Township in Wyoming County. The surficial geology in the vicinity of the stream consists mainly of Wisconsinan Till, bedrock, alluvium, wetlands, and a lake. A number of bridges have been constructed across it. The stream is classified as a Coldwater Fishery and a Migratory Fishery.