The state highway passes through the area patented in the 18th century as My Lady's Manor.

The state highway passes through Troyer and curves along a ridge above the headwaters of Little Gunpowder Falls.

Troyer Road continues east on the other side of the intersection as a county highway.

[5][6] The gap in the improved road through Monkton was filled in 1928 and a bridge for the Northern Central Railroad to cross over MD 138 was built shortly after 1930.

[11][12] MD 138 from just west of Gunpowder Falls through Monkton to east of Wesley Chapel Road was transferred from state to county maintenance in 1968.