Mercersburg, Pennsylvania, 17236. Population 1540. Located in southwest Franklin County just north of the Mason-Dixon Line. Our 15th President, James Buchanan, was born in Cove Gap, just on the outskirts of Mercersburg and grew up in town. His log cabin still stands on the grounds of Mercersburg Academy. Also, William Findlay, Governor of Pennsylvania from 1817 until 1820 was born in 1768 in Mercersburg.