What is currently US 9 in Delaware existed as a state highway between Whaleys Corners and Georgetown by 1920, with the remainder as an unimproved county road. At the time, the road was a state aid highway between Laurel and Whaleys Corners and under contract as a state aid highway between Georgetown and Harbeson. By 1924, the state highway along the present alignment of US 9 was completed, running from Laurel through Georgetown to Lewes. A year later, what is now US 9 along the DE 1 concurrency between Wescoats Road and Carpenters Corner was built as a state highway. The Kings Highway portion of the current route was paved by 1931. When Delaware assigned numbers to its state highways by 1936, DE 28 was designated to run from US 13 (Central Avenue) in Laurel to DE 18 in Georgetown while the road between Georgetown and Lewes became a part of DE 18. By 1954, US 13 was moved to a new alignment to the east of Laurel, and the western terminus of DE 28 was truncated from Central Avenue to the new location of US 13. The same year, the present alignment of US 9 between Five Points and Wescoats Road was constructed as part of a new divided highway alignment of DE 14.