Libertytown to Thurmont MD 550 begins at an intersection with MD 26 (Main Street) in the
unincorporated village of Libertytown and heads northwest as Woodsboro Road. The highway passes through the Piedmont uplands, a region of rounded hills, low ridges, relatively high relief, irregular plains, and narrow valleys with a mix of farms and forests. MD 550 crosses Cabbage Run and Dorcas Branch, follows Dorcas Branch through a gap in Laurel Hill, and enters the town of Woodsboro just after crossing Israel Creek. MD 550 turns north and
runs concurrently with
MD 194 on Woodsboro Pike on the east side of the town; Liberty Road heads west from the intersection toward the center of town. MD 550 turns west onto Woodsboro–Creagerstown Road, which immediately intersects the north end of Main Street (MD 194A). MD 550 continues northwest through the Piedmont lowlands, which contain wide and undulating ridges, broad nearly level valleys, limited local relief, and a mosaic of farms, houses, and woodland. MD 550 also passes to the west of another 18th century farmhouse,
Strawberry Hill, before reaching the unincorporated village of Creagerstown. The route’s name changes to Creagerstown Road at Old Frederick Road at the south end of village, and at Blacks Mill Road the road passes to the east of the
St. John's Church at Creagerstown Historic District, which preserves a pair of church buildings—the early 20th-century St. John’s Evangelical Lutheran Church and the 19th-century building of the defunct St. John’s Reformed Church—as well as the first church’s parish house and a cemetery. MD 550 continues northwest as Creagerstown Road to the hamlet of Jimtown; the highway intersects Moser Road and Hessong Bridge at a four-legged intersection and turns north onto Jimtown Road toward Thurmont. At the northern edge of Thurmont, the state highway meets US 15 (Catoctin Mountain Highway) at a
diamond interchange and passes
Catoctin High School. After passing through the unincorporated village of Sabillasville and intersecting Bentzel Road on the north side of the village, the highway leaves the valley and ascends the eastern flank of South Mountain. MD 550 curves west parallel to the Maryland Midland Railway and summits
South Mountain at the Frederick–Washington county line about south of the
Pennsylvania state line. The highway intersects
CSX's
Hanover Subdivision rail line at grade, turns from McAfee Hill Road onto Pen Mar Road, and passes under the railroad and by Lake Royer. MD 550 reaches its northern terminus west of the lake at the edge of Camp Louise, a girls' summer camp founded in 1922; Pen Mar Road continues as a county highway toward the community of Pen Mar and
Pen Mar Park. ==History==