Known for most of its length as Governor Run Road, the state highway runs 1.14 miles (1.83 km) from MD 2/MD 4 east to a dead end at the Chesapeake Bay within Port Republic.

The two state highways run concurrently southeast along St. Leonard Road for a short distance before MD 509 splits east onto Governor Run Road.

The highway heads east as a two-lane undivided road through a forested area split by a trio of transmission lines that extend north from the Calvert Cliffs Nuclear Power Plant.

After crossing Governor Run, the state highway reaches its eastern terminus at a dead end just west of the Chesapeake Bay shoreline.

[4][5] The entire route is in Port Republic, Calvert County.