 What is now DE 9A was a county road by 1920. By 1924, the Christiana Avenue portion of the route was constructed as a state highway. Christiana Avenue became a portion of US 40 in 1926, running from US 13 to a ferry that went across the Delaware River to Penns Grove, New Jersey. By 1931, US 40 was removed from this road. The road became the easternmost portion of DE 48 by 1936, which crossed the Delaware River on the ferry to connect to New Jersey Route 48 in Penns Grove. DE 48 was removed from this road by 1952 after the ferry between Wilmington and Penns Grove was discontinued in 1949. DE 9A was designated around 1971 onto its current alignment.
