Dauphin is located on the western edge of Dauphin County at , on the east bank of the Susquehanna River. The land at the river's edge is alluvial floodplain, but Dauphin sits at the head of a narrow valley between two mountains, at the mouth of Stony Creek. The valley between the two mountains is called Stony Valley, which contains the villages of Singersville and Ellendale Forge. This section along the Susquehanna River is a gateway from the southeastern plains into the Appalachian Mountains and the north-central part of the state. Berrier Island is also located at Dauphin.