(This article is about the section of U.S. Route 15 in Maryland. For the entire route, see U.S. Route 15.) U.S. Route 15 (US 15) is a part of the U.S. Highway System that runs from Walterboro, South Carolina to Painted Post, New York. In Maryland, the highway runs 37.85 miles (60.91 km) from the Virginia state line at the Potomac River in Point of Rocks north to the Pennsylvania state line near Emmitsburg. Known for most of its length as Catoctin Mountain Highway, US 15 is the primary north–south highway of Frederick County. The highway connects the county seat of Frederick with Point of Rocks, Leesburg, Virginia, and Charles Town, West Virginia (via US 340), to the south and with Thurmont, Emmitsburg, and Gettysburg, Pennsylvania, to the north. US 15 is a four-lane divided highway through