Geography Middlesex Township is in northeastern Cumberland County, bordered to the north by Perry County along the crest of Blue Mountain. Conodoguinet Creek, a tributary of the Susquehanna River, crosses the center of the township. Unincorporated communities in the township include Donnellytown in the northeast, Carlisle Springs in the northwest, and part of the Schlusser census-designated place along the western border.
Geography Middlesex Township is in northeastern Cumberland County, bordered to the north by Perry County along the crest of Blue Mountain. Conodoguinet Creek, a tributary of the Susquehanna River, crosses the center of the township. Unincorporated communities in the township include Donnellytown in the northeast, Carlisle Springs in the northwest, and part of the Schlusser census-designated place along the western border