The state highway runs 24.43 miles (39.32 km) from MD 26 in Libertytown north to Pen Mar Road in Fort Ritchie.

The highway from Thurmont to Blue Ridge Summit was constructed in the mid-1920s as Maryland Route 81 (MD 81).

[2] 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.

[1][2] The state highway intersects the MDOT Branch of the Maryland Midland Railway and receives the north end of Creagerstown Road before leaving Woodsboro.

[2][6] 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.

[2][7] MD 550 also passes to the west of another 18th century harmhouse, Strawberry Hill, before reaching the unincorporated village of Creagerstown.

The two state highways run concurrently northwest toward downtown Thurmont on Main Street.

[1][2] The Victor Cullen Center is a state youth detention center originally constructed in the first decade of the 20th century as the state’s first tuberculosis sanatorium, whose preserved historic remains include the power house and old administration building.

[18][19] The first section of MD 550 proper was 1 mile (1.6 km) of concrete road built east from Woodsboro in 1933.

[20] The eastern end of Military Road at the Frederick–Washington county line was tied into a relocation of MD 81 between Sabillasville and Blue Ridge Summit that was completed in 1936.

[31] When the bypass was completed in 1997, MD 550 was removed from the center of Woodsboro to its present alignment on the northern and eastern sides of town.