Selinsgrove is the largest borough in Snyder County, Pennsylvania, United States. The population was 5,383 at the 2000 census.Selinsgrove is located in the middle of the Susquehanna River Valley in Central Pennsylvania, along U.S. Routes 11 and 15, 50 miles north of Harrisburg and about 5 miles southwest of Sunbury. It is the home of Susquehanna University.