Letterkenny Township is a township that is located in Franklin County, Pennsylvania, United States. The population was 2,462 at the time of the 2020 census, up from 2,074 at the 2000 census. The township is named after Letterkenny in County Donegal, Ireland. The Horse Valley Bridge, Rocky Spring Presbyterian Church, and Skinner Tavern are listed on …Letterkenny Township is a township that is located in Franklin County, Pennsylvania, United States. The population was 2,462 at the time of the 2020 census, up from 2,074 at the 2000 census. The township is named after Letterkenny in County Donegal, Ireland. The Horse Valley Bridge, Rocky Spring Presbyterian Church, and Skinner Tavern are listed on the National Register of Historic Places.