The highway was extended south to Smithsburg along a partially new alignment in the early 1960s, replacing a road that had been designed MD 92 from the mid-1930s to the mid-1950s.

The state highway heads northeast as two-lane undivided Raven Rock Road, which flanks the western slope of South Mountain and parallels CSX's Hanover Subdivision railroad line.

MD 491 veers east away from the railroad at Fruit Tree Drive and crosses Little Antietam Creek.

The state highway continues north to a four-way intersection next to the historic summer cottage Tipahato.

MD 491 turns west onto Macfee Hill Road into Washington County.

[5] MD 92 was rebuilt around 1944 as a military access project, as the state highway was part of the most direct route between Hagerstown and Fort Ritchie.