The first section of MD 405 to be constructed was a stretch of concrete road southeast from the Centreville Branch of the
Philadelphia, Baltimore and Washington Railroad at Price in 1929 and 1930. The concrete road was extended southeast in two sections, the first one started in 1930. The second section was completed through Roe in 1932. The first section of the concrete road connecting Price and MD 19 was built south from MD 19 to Granny Branch Road in 1933; this work involved reconstruction of the MD 19–MD 405 intersection. The gap between Church Hill and Price was filled with another stretch of concrete road in 1934. The remainder of Price Station Road and what is now MD 304 east to Mason Branch of
Tuckahoe Creek were added to the state system as an extension of MD 405 through a February 26, 1942,
Maryland State Roads Commission resolution after the state had improved the county roads to state standards starting in 1940. The highway reached its greatest extent when the roads commission authorized the transfer of the Bridgetown Road from Mason Branch to
MD 312 at Bridgetown from county to state control through an August 22, 1957, resolution. Caroline County had constructed with state aid the two-span reinforced concrete Mason Branch bridge and a shell road east through Bridgetown in 1914. The state extended MD 304 east from Ruthsburg to the MD 304–MD 405 junction through a February 19, 1962, memorandum of action. MD 304 then took over the portion of MD 405 to Bridgetown in 1969. MD 405 was resurfaced with bituminous concrete from MD 19 to Price in 1970 and from Price to MD 304 in 1974. ==Junction list==