U.S. Route 9 (US 9) is a U.S. highway in the northeast United States, running from Laurel, Delaware north to Champlain, New York. In Delaware, the route runs an east–west 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 to the Cape May-Lewes Ferry across the Delaware Bay in Lewes, which carries the route to 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 in Five Points. Between Georgetown and Five Points, US 9 runs concurrent with DE 404.

What is now US 9 in Delaware was originally built as a state highway during the 1920s and designated by 1936 as DE 28 between Laurel and Georgetown and a part of DE 18 between Georgetown and Lewes. US 9 was extended to Delaware from New Jersey by way of the Cape May-Lewes Ferry by 1976, replacing all of DE 28 and the portion of DE 18 between Georgetown and Five Points, with the route aligned to bypass Lewes. DE 404 was designated along the portion of US 9 between Georgetown and Five Points by 1987.

US 9 starts out at an intersection with US 13 in the commercial northern part of Laurel, heading to the northeast on two-lane undivided County Seat Highway. The road leaves Laurel and heads through a mix of farmland and woodland with some homes. The route intersects DE 20 in Hardscrabble, at which point it briefly becomes a divided highway. Past this intersection, US 9 becomes undivided again and passes through agricultural areas with some woods and residences. Farther northeast, the road reaches Georgetown and intersects US 113 in a commercial area. At this point, US 9 Truck heads south along US 113 to bypass Georgetown to the south. Following US 113, the route continues northeast on West Market Street, passing homes and a few businesses. US 9 heads into the commercial center of Georgetown and intersects DE 18/DE 404 at The Circle.

At this point, US 9 continues northeast concurrent with DE 404 on East Market Street, lined with downtown businesses. The road crosses Norfolk Southern's Indian River Secondary railroad line and runs through residential areas with a few commercial establishments. US 9/DE 404 heads east-northeast out of Georgetown and becomes Lewes Georgetown Highway, passing through farmland with some homes and businesses. The two routes intersect the eastern terminus of US 9 Truck and run through wooded areas with some fields and development. In Gravel Hill, the road intersects DE 30. Following this intersection, US 9/DE 404 passes through more farmland and woodland with some residences, reaching a junction with DE 5 in Harbeson. The two routes run through more rural areas, crossing a Delaware Coast Line Railroad line. The road heads through farmland with increasing residential subdivisions. Upon reaching the area of the Five Points intersection in Nassau, US 9/DE 404 runs past homes and businesses, widening into a divided highway and coming to an intersection with DE 1D/DE 23. DE 23 joins US 9/DE 404 for a concurrency on a four-lane divided highway before the road comes to a junction with DE 1. Here, DE 23/DE 404 ends, US 9 Bus. continues northeast, and US 9 heads east for a concurrency with DE 1.

Past the Five Points intersection, US 9 follows DE 1 on the six-lane divided Coastal Highway, running through commercial areas. The road curves southeast into wooded areas with some businesses. In Carpenters Corner, US 9 splits from DE 1 by turning northeast onto Dartmouth Drive, a three-lane undivided road with two westbound lanes and one eastbound lane. A short distance later, the route turns north-northeast onto two-lane undivided Kings Highway, passing through farmland with some residential subdivisions. US 9 splits from Kings Highway and continues northeast on Theodore C. Freeman Memorial Highway, bypassing Lewes to the southeast. The route runs through areas of trees, crossing the Lewes and Rehoboth Canal on a high-level bridge. The road passes through more woods and turns north, crossing the Delaware Coast Line Railroad. After the railroad tracks, US 9 intersects US 9 Bus. again and turns east onto Cape Henlopen Drive, running between residential development along the Delaware Bay to the north and the railroad tracks to the south. US 9 comes to the terminal of the Cape May-Lewes Ferry, which carries the route across the Delaware Bay to Cape May, New Jersey.

US 9 in Delaware has an annual average daily traffic count ranging from a high of 53,789 vehicles along the DE 1 concurrency to a low of 895 vehicles at the Cape May-Lewes Ferry terminal. The portion of US 9 in Delaware east of DE 18/DE 404 in Georgetown is part of the National Highway System.

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. By 1925, what is now US 9 along the DE 1 concurrency 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 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 to the new location of US 13. The Cape May-Lewes Ferry was started in 1964; at this time, the ferry did not carry a route number. By this time, the Theodore C. Freeman Highway portion of US 9 had been built.

By 1976, US 9 was extended across the ferry from New Jersey to Delaware, replacing DE 28 between Laurel and Georgetown and DE 18 between Georgetown and Five Points. Between Five Points and the terminal of the Cape May-Lewes Ferry, US 9 followed DE 14 (now DE 1), Kings Highway, and Theodore C. Freeman Highway before coming to Cape Henlopen Drive. At the same time, US 9 Business was designated onto the former alignment of DE 18 between Five Points and Lewes as well as a portion of Cape Henlopen Drive connecting to US 9. US 9 Truck was created as a truck bypass of the portion of US 9 through Georgetown by 1984. DE 404 was extended to follow US 9 between Georgetown and Five Points by 1987.