Chambersburg is a borough in and the county seat of Franklin County, in the South Central region of Pennsylvania, United States. It is in the Cumberland Valley, which is part of the Great Appalachian Valley, and 13 miles north of Maryland and the Mason-Dixon line and 52 miles southwest of Harrisburg, the state capital. According to the United States Census Bureau, Chambersburg's 2020 population was 21,903. When combined with the surrounding Greene, Hamilton, and Guilford Townships, the population of Greater Chambersburg is 52,273 people. The Chambersburg, PA Micropolitan Statistical Area includes surrounding Franklin County, and in 2010 included 149,618 people.
According to the Pennsylvania Department of Community and Economic Development, Chambersburg Borough is the thirteenth-largest municipality in the Commonwealth of Pennsylvania and the largest Borough, as measured by fiscal size. Chambersburg Borough is organized under the Pennsylvania Borough Code and is not a home-rule municipality.
Chambersburg's settlement began in 1730 when water mills were built at Conococheague Creek and Falling Spring Creek. The town developed on both sides of these creeks.