Delaware Run is a tributary of the West Branch Susquehanna River in Northumberland County, Pennsylvania, in the United States. It is 7.4 miles (11.9 km) long. It flows through Delaware Township, starting in the Muncy Hills. The watershed has an area of 11.7 square miles in Northumberland and Lycoming Counties. Delaware Run was reached by Europeans as early as 1737 and an area near it settled in 1769 and the community of Dewart is near Delaware Run.