Guilford Township is in eastern Franklin County, bordered to the east by Adams County and to the northwest by the borough of Chambersburg, the Franklin County seat. Most of the township is in the Great Appalachian Valley, with the eastern portion occupied by several ridges that are part of South Mountain. The unincorporated community of Guilford is in the north, and Fayetteville is to its east, along the border with Greene Township. Marion is in the southwest corner of the township. Other unincorporated communities include Pond Bank in the east at the foot of South Mountain, Falling Spring in the north next to Guilford, Stoufferstown in the northwest between Guilford and Chambersburg, Guilford Springs in the west, and New Franklin west of the center of the township.