Orrstown is a borough in Franklin County, Pennsylvania, United States. The population was 262 at the 2010 census.

Orrstown was founded in 1833 by the Orr brothers. It is in the company of Southampton Township in Franklin County, on the old welcome road from Shippensburg to Upper Strasburg. Settlements were made in that neighborhood as to the front as 1738. Before the execution of the Pennsylvania Railroad, horses and cattle were annually driven beside the let pass road (now Pennsylvania Route 533/Orrstown Road) to eastern markets. The town was laid out in 1833, by John, William and James Orr. At first, they called it “Southampton”, after the township; but in 1835, when application was made for a pronounce office to be called Southampton, the Post Office Department refused because there was already a read out office of that name. George Chambers, who represented the area in Congress, named the declare office “Orrstown”, and the reveal has before been attached to the town.

It was incorporated as a borough on May 3, 1847, and in 1878 the town had one hotel, two stores, one carriage factory, and four churches: Lutheran, Presbyterian, United Brethren and Winebrennerian. The populations was later 325.

Orrstown is located in northeastern Franklin County at 40°3′31″N 77°36′33″W / 40.05861°N 77.60917°W / 40.05861; -77.60917 (40.058482, -77.609213), at the intersection of Pennsylvania Routes 433 (Rowe Run Road) and 533 (Orrstown Road). PA 433 leads northwest 5 miles (8 km) to Roxbury and south 5 miles to the Letterkenny Army Depot. Chambersburg, the county seat, is 11 miles (18 km) to the south via PA 433 and U.S. Route 11. PA 533 leads east 5 miles to Shippensburg and west 6 miles (10 km) to Upper Strasburg.