MD 312 traverses northwestern Caroline County, connecting Ridgely with Bridgetown.

MD 312 heads north as two-lane undivided Downes Station Road, passing through farmland until it curves to the east and meets MD 480 (Ridgely Road) on a tangent, joining that highway in a concurrency.

[1][2] The first section of MD 312 was paved through Ridgely and north about 1 mile (1.6 km) toward Oakland by 1921.

[4] The state highway was constructed between MD 404 at Long's School House Corner and Ridgely in 1924 and 1925.

[5][6] The remainder of the highway through Bridgetown to MD 313 at Baltimore Corner was constructed between 1926 and 1929.