Herndon, formerly Trevorton Junction, is a borough along the Susquehanna River in Northumberland County, Pennsylvania, United States. Herndon was first founded by Robert A. Parrish in 1840. The town was later named for Naval commander William Lewis Herndon, who died in 1857 while trying to rescue passengers from his sinking ship. The population was 324 at the 2010 census.
Herndon is located at 40°42′15″N 76°50′36″W (40.704241, -76.843212).
According to the United States Census Bureau, the borough has a total area of 1.8 square miles (4.7 km2), of which, 0.8 square miles (2.1 km2) of it is land and 1.0 square mile (2.6 km2) of it (55.06%) is water.
At the 2000 census there were 383 people, 173 households, and 106 families residing in the borough. The population density was 477.6 people per square mile (184.8/km2). There were 192 housing units at an average density of 239.4 per square mile (92.7/km2). The racial makeup of the borough was 97.91% White, 1.83% African American, and 0.26% from two or more races. There were 173 households, 20.2% had children under the age of 18 living with them, 56.1% were married couples living together, 4.0% had a female householder with no husband present, and 38.2% were non-families.