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 (21 km) north of Maryland and the Mason-Dixon line and 52 miles (84 km) 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 Metropolitan 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 Pennsylvania and the largest borough as measured by fiscal size as of 2016. 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. Its history includes episodes relating to the French and Indian War, the Whiskey Rebellion, John Brown's raid on Harpers Ferry, and the Civil War. The borough was the only major northern community burned down by Confederate forces during the war. Residents charged the Confederates with war crimes.

Chambersburg is served by the Lincoln Highway, U.S. 30, between McConnellsburg and Gettysburg. U.S. 11, the Molly Pitcher Highway, passes through it between Shippensburg, Pennsylvania, and Hagerstown, Maryland. Interstate 81 skirts the borough to its east. The town lies approximately midpoint on US Route 30 between Pittsburgh and Philadelphia. The local topography reflects both flatter areas like Philadelphia and mountainous areas like Pittsburgh. Downtown Chambersburg has occasional events such as Food Truck Festival and Apple Fest.