The section of the present route between New Castle and Wilmington was constructed as the New Castle and Wilmington Turnpike, a private turnpike, in 1813. What would become DE 9 originally existed as a county road by 1920. Four years later, the road between Leipsic and Smyrna was upgraded to a state highway. In addition, the current alignment of DE 9 around Taylors Bridge and between Delaware City and Wilmington was paved. In 1931, what would become DE 9 was upgraded to a state highway between Bay Road and Little Creek and between Port Penn and Delaware City. A year later, the road became a state highway between Delaware City and Wilmington. By this time, what would become DE 9 between Little Creek and Leipsic was upgraded to a state highway. A drawbridge was constructed over the Delaware City Channel in 1933. This drawbridge was sealed and rendered inoperable in 1971.