Codorus Creek attracted the area's first European settlers, who used its water to power mills, and its flat floodplain also proved ideal for trains. In 1839, the Baltimore and Susquehanna, forerunner of the Northern Central Railway, built a station nearby, and the small settlement soon became a real town, receiving its own post office in 1843. Access to trains allowed the mills to expand their business, and by the 1880s Glen Rock produced flour, rope, twine, window sashes, and carriages. The town was originally called Heathcote Station after the man who owned most of the area, but William Heathcote suggested the name Glen Rock, referring both to the town's location in a glen and to a prominent rock outcrop exposed by railroad construction. Glen Rock is naturally prone to flooding because Codorus Creek runs through the town's center and rainwater races down the steep surrounding hills into the stream; in 1972, Hurricane Agnes caused the worst flood in the town's history.