The road continues southeast as High Street toward the Chestertown Historic District. The Chestertown–Rock Hall highway was one of the roads the Maryland State Roads Commission designated for improvement in 1909, but by 1915 the highway was not deemed an essential part of the main system. The highway from Fairlee to near Broad Neck Road was paved as a macadam road in 1915. The gap between Fairlee and Chestertown was filled when a concrete road was built from near Broad Neck Road to College Avenue in Chestertown and along Spring Avenue between High Street and Maple Avenue in 1917 and 1918. In addition, concrete road was constructed from Fairlee to Edesville in 1918. The highway from Edesville to Rock Hall was under construction by 1920 and completed by 1921. The Edesville–Rock Hall segment, which followed Sharp Street and Main Street in the town of Rock Hall, was built of concrete except for near the Rock Hall–Bay Shore ferry, which was built with macadam to allow ferry traffic to use the highway during construction. As early as 1923 and late as 1928, a ferry connected Rock Hall with Bay Shore Park near Fort Howard in Baltimore County, thus briefly and indirectly connecting this MD 20 with the former MD 20 in Baltimore County. MD 20 was widened and resurfaced with bituminous concrete from Chestertown to Rock Hall in 1947 and 1948. Spring Avenue in Chestertown was resurfaced with bituminous concrete in 1950, and MD 20's bridge across Radcliffe Creek was replaced that year and 1951. MD 20's bypass of Fairlee was constructed in 1953; the bypassed segments became a southern extension of MD 298 and MD 298A on Old Fairlee Road. The highway bypassed the center of Rock Hall when Rock Hall Avenue from MD 445 to Sharp Street just east of town was built in 1959 and 1960, leaving behind MD 674 on Sharp Street. MD 20 was reconstructed from MD 288 to MD 298, including eliminating a curve, in 1976. MD 20 was reconstructed from Radcliffe Creek to the MD 291 junction when the latter highway was extended west to its present terminus in 1968 and 1969. The MD 20 portion of High Street from MD 291 to College Avenue was reconstructed in 1979. The portions of MD 20 on High Street from MD 291 to College Avenue and on Spring Avenue were transferred from state to municipal maintenance through an August 27, 1985, road transfer agreement. The portion of High Street from College Avenue to Spring Avenue had already been municipally maintained. In 2014, a roundabout was constructed at the MD 20–MD 291 junction.