The gap between Octoraro Creek and the east limit of Rising Sun was under construction in 1919 and completed by 1921, providing an all-weather road between the Conowingo Bridge and halfway between Calvert and Blue Ball. The section of MD 273 between Appleton and the Delaware state line was also paved by 1921. The western section of modern road was extended through Blue Ball by 1923. The remaining highway between Calvert and Fair Hill was constructed between 1924 and 1926. The final piece of MD 273 was completed between Fair Hill and Appleton in 1930. US 1 was assigned to the section of the state road west of Sylmar Road and MD 273 was later marked on the eastern portion to Newark. MD 273 was also marked on the portion of the original state road between the defunct Conowingo Bridge and Octoraro Creek—Old Conowingo Road, Ragan Road, and Connelly Road—left behind when US 1 was moved to a new alignment serving Conowingo Dam in 1928.