Maryland Route 550 (MD 550) is a state highway in the U.S. state of Maryland. The state highway runs 24.43 miles (39.32 km) from MD 26 in Libertytown north to Pen Mar Road in Fort Ritchie. MD 550 runs southeast–northwest across central Frederick County, connecting Fort Ritchie in the northeastern corner of Washington County and Libertytown with the towns of Thurmont and Woodsboro and the smaller communities of Creagerstown and Sabillasville. South of the highway's junction with U.S. Route 15 (US 15) in Thurmont, the state highway passes through the wide valley of the Monocacy River; to the north, the highway passes along the northern edge of Catoctin Mountain and crests South Mountain near Blue Ridge Summit, Pennsylvania.