Duncannon is a borough in Perry County, Pennsylvania, United States. The population was 1,473 at the 2020 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.

Perry County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 45,842. The county seat is New Bloomfield. The county was created on March 22, 1820, and was named for Oliver Hazard Perry, a hero of the War of 1812, who had recently died. It was originally part of Cumberland County and was created in part because residents did not want to travel over the mountain to Carlisle, the county seat of Cumberland County. Landisburg became the temporary county seat before New Bloomfield was ultimately chosen. The county is part of the South Central Pennsylvania region of the state.