U.S. Route 9 (US 9) is a United States Numbered Highway in the Northeastern U.S., running from Laurel, Delaware, north to Champlain, New York. In Delaware, the route runs a southwest–northeast path through Sussex County. Even though US 9 is signed north–south for the remainder of its route, the segment in Delaware is signed east–west. The highway runs from its western terminus at US 13 in Laurel northeast to the Cape May–Lewes Ferry terminal in Lewes, where the ferry carries the route across the Delaware Bay to North Cape May, New Jersey. US 9 passes through rural areas and serves the communities of Laurel, Georgetown, and Lewes. US 9 intersects Delaware Route 20 (DE 20) in Hardscrabble, US 113 and DE 18/DE 404 in Georgetown, DE 30 in Gravel Hill, DE 5 in Harbeson, and DE 1 at the Five Points intersection in Nassau. US 9 runs concurrent with DE 404 between Georgetown and Five Points and with DE 1 between Five Points and Carpenters Corner.

Sussex County is located in the southern part of the U.S. state of Delaware, on the Delmarva Peninsula. As of the 2020 census, the population was 237,378, making it the state's second most populated county only behind New Castle and ahead of Kent. The county seat is Georgetown.