Duncannon is a borough in Perry County, Pennsylvania, United States. The population was 1,522 at the 2010 census. It is part of the Harrisburg–Carlisle Metropolitan Statistical Area. The center of population of Pennsylvania is located in Duncannon. Lightning Guider sleds were manufactured in Duncannon from 1904 until 1988. The Appalachian Trail makes its way through the town, going on various streets, and runs mainly along North High Street. It comes off the mountain at 40.3813, -77.0292 lat/long, onto Inn Road.
Duncannon was originally called Petersburg, and under the latter name was laid out in 1792. The present name is derived from Duncan's Island in the Susquehanna River.
The Puritan missionary David Brainerd visited the area in the 1740s. In his journal he describes his trip on the Susquehanna and his brief stay with an Indian tribe on Duncan's Island, across the river from present-day Duncannon.