Fallow Hollow is an unofficially named tributary of Coles Creek in Columbia County, Pennsylvania, in the United States. It is approximately 1.5 miles (2.4 km) long and flows through Sugarloaf Township. The watershed of the stream has an area of 0.96 square miles (2.5 km2). Fallow Hollow is listed on the Columbia County Natural Areas Inventory as a "Locally Significant Area". The stream is also Class A Wild Trout Waters.