The first two improved sections of what is now MD 304 were county-constructed highways built with state aid.
Caroline County built the two-span reinforced concrete Mason Branch bridge and a 9-foot-wide (2.7 m) shell road east through Bridgetown in 1914.
Queen Anne's County paved Water Street as a 14-foot-wide (4.3 m) concrete road from west of Commerce Street to the Centreville Branch of the Philadelphia, Baltimore and Washington Railroad and built a 9-foot-wide (2.7 m) shell road from the railroad to about 2 miles (3.2 km) east of downtown between 1915 and 1921.
The Maryland State Roads Commission extended the concrete road from Water Street west to Centreville Landing, the wharf serving the county seat, in 1924 and 1925.
The state reconstructed the 1910s county-built shell road east from the railroad as a macadam road in two segments in 1934 and 1935.
Another 1-mile-long (1.6 km) section was built east from the end of the macadam reconstruction starting in 1936, and another 1.5-mile-long (2.4 km) segment was constructed by 1938.
The Maryland State Roads Commission extended MD 304 to MD 481 at Ruthsburg through a February 26, 1942, resolution after the 2-mile-long (3.2 km) county section west from Ruthsburg was improved to state standards.
The portion of MD 304 east 2 miles (3.2 km) from the Centreville town limit was reconstructed between 1946 and 1948.

A 2.27-mile-long (3.65 km) macadam road was built west from Centreville Landing along Corsica Neck in 1935, and a new bridge was built across the Old Mill Stream Branch of the Corsica River in 1936 and 1937.
Corsica Neck Road was designated MD 606 until the MD 304 designation was extended west from Centreville Landing in 1950.
Before that extension, the portions of MD 606 from its MD 304 junction west to the town limit and MD 304 itself in Centreville were resurfaced in 1949.
On August 13, 1952, the town of Centreville agreed to municipally maintain Chesterfield Avenue and the portion of Water Street west of Liberty Street in exchange for the roads commission taking over maintenance of Liberty Street so that street could be the southbound direction of a US 213 one-way pair.
After the state resurfaced the portion of Water Street east of Liberty Street and Railroad Avenue east to the town limit and reconstructed the intersection of Commerce and Water streets, the town agreed to take over the remainder of MD 304 in town through a June 26, 1958 agreement.

The Maryland State Roads Commission brought the portion of MD 304 from MD 481 to MD 405 into the state highway system through a February 19, 1962, memorandum of action.
MD 304 from the current MD 405 intersection to the county line had been brought into the state system as an extension of MD 405 in the same resolution that extended MD 304 to Ruthsburg in 1942.
The state and Caroline County agreed to bring Bridgetown Road from the county line to MD 312 into the state system as an extension of MD 405 through an August 22, 1957, resolution.
MD 304 replaced MD 405 from the MD 405 intersection to MD 312 in 1969.
That same year and extending into 1970, the highway was reconstructed from the east town limit of Centreville to US 301.
MD 304 was resurfaced with bituminous concrete from US 301 to MD 481 in 1972 and from MD 481 to Mason Branch in 1977.
The 1930s Corsica River bridge was replaced with the current steel beam bridge between 1984 and 1986.
Water Street from west of Liberty Street to Commerce Street was made one way in 1997 or 1998.

MD 304A was designated along the portion of MD 304 east of US 301 when the superstreet intersection between the two highways was installed in 2011.
The Maryland Department of Transportation built a dumbbell interchange to replace the superstreet intersection with US 301.
The interchange project constructed a bridge carrying MD 304 over US 301.
This interchange was the top transportation priority for Queen Anne's County for years and was pushed for by students at Queen Anne's County High School after a student at the school was killed in an accident at the intersection in 2010.
A groundbreaking
The first two improved sections of what is now MD 304 were county-constructed highways built with state aid. Caroline County built the two-span reinforced concrete Mason Branch bridge and a 9-foot-wide (2.7 m) shell road east through Bridgetown in 1914. Queen Anne's County paved Water Street as a 14-foot-wide (4.3 m) concrete road from west of Commerce Street to the Centreville Branch of the Philadelphia, Baltimore and Washington Railroad and built a 9-foot-wide (2.7 m) shell road from the railroad to about 2 miles (3.2 km) east of downtown between 1915 and 1921. The Maryland State Roads Commission extended the concrete road from Water Street west to Centreville Landing, the wharf serving the county seat, in 1924 and 1925. The state reconstructed the 1910s county-built shell road east from the railroad as a macadam road in two segments in 1934 and 1935. Another 1-mile-long (1.6 km) section was built east from the end of the macadam reconstruction starting in 1936, and another 1.5-mile-long (2.4 km) segment was constructed by 1938. The Maryland State Roads Commission extended MD 304 to MD 481 at Ruthsburg through a February 26, 1942, resolution after the 2-mile-long (3.2 km) county section west from Ruthsburg was improved to state standards. The portion of MD 304 east 2 miles (3.2 km) from the Centreville town limit was reconstructed between 1946 and 1948.
A 2.27-mile-long (3.65 km) macadam road was built west from Centreville Landing along Corsica Neck in 1935, and a new bridge was built across the Old Mill Stream Branch of the Corsica River in 1936 and 1937. Corsica Neck Road was designated MD 606 until the MD 304 designation was extended west from Centreville Landing in 1950. Before that extension, the portions of MD 606 from its MD 304 junction west to the town limit and MD 304 itself in Centreville were resurfaced in 1949. On August 13, 1952, the town of Centreville agreed to municipally maintain Chesterfield Avenue and the portion of Water Street west of Liberty Street in exchange for the roads commission taking over maintenance of Liberty Street so that street could be the southbound direction of a US 213 one-way pair. After the state resurfaced the portion of Water Street east of Liberty Street and Railroad Avenue east to the town limit and reconstructed the intersection of Commerce and Water streets, the town agreed to take over the remainder of MD 304 in town through a June 26, 1958 agreement.
The Maryland State Roads Commission brought the portion of MD 304 from MD 481 to MD 405 into the state highway system through a February 19, 1962, memorandum of action. MD 304 from the current MD 405 intersection to the county line had been brought into the state system as an extension of MD 405 in the same resolution that extended MD 304 to Ruthsburg in 1942. The state and Caroline County agreed to bring Bridgetown Road from the county line to MD 312 into the state system as an extension of MD 405 through an August 22, 1957, resolution. MD 304 replaced MD 405 from the MD 405 intersection to MD 312 in 1969. That same year and extending into 1970, the highway was reconstructed from the east town limit of Centreville to US 301. MD 304 was resurfaced with bituminous concrete from US 301 to MD 481 in 1972 and from MD 481 to Mason Branch in 1977. The 1930s Corsica River bridge was replaced with the current steel beam bridge between 1984 and 1986. Water Street from west of Liberty Street to Commerce Street was made one way in 1997 or 1998.
MD 304A was designated along the portion of MD 304 east of US 301 when the superstreet intersection between the two highways was installed in 2011. The Maryland Department of Transportation built a dumbbell interchange to replace the superstreet intersection with US 301. The interchange project constructed a bridge carrying MD 304 over US 301. This interchange was the top transportation priority for Queen Anne's County for years and was pushed for by students at Queen Anne's County High School after a student at the school was killed in an accident at the intersection in 2010. A groundbreaking
Maryland Route 304