 Kelly Township is bordered by White Deer Township to the north, the West Branch Susquehanna River to the east, across which lies Northumberland County (more specifically, the Borough of Milton and West Chillisquaque Township), Lewisburg to the south and Buffalo Township to the south and west.As of the census of 2000, there were 4,502 people, 1,313 households, and 778 families residing in the township.The population density was 262.6 people per square mile (101.4/km²).