Delaware Route 42 (DE 42) is a state highway in Kent County, Delaware. It runs from DE 6 in Blackiston east to DE 9 in Leipsic. DE 42 passes through rural areas along with the towns of Kenton and Cheswold. The route intersects DE 300 in Kenton, DE 15 between Seven Hickories and Moores Corner, and U.S. Route 13 (US 13) in Cheswold. The road was built as a state highway during the 1920s and 1930s. DE 42 was designated by 1936 between Kenton and Leipsic and extended to Blackiston by 1966.

DE 42 begins at an intersection with DE 6 in Blackiston. Northwest of DE 6, the road continues as Longridge Road, which runs to the Maryland border where it becomes Maryland Route 330 (MD 330). MD 330 heads west through Kent County, Maryland and, by way of MD 313, provides access to US 301. From the western terminus, DE 42 heads southeast on two-lane undivided Blackiston Road. The route passes through agricultural areas with some woods and homes. The road reaches Kenton, where it becomes Commerce Street. In Kenton, the route crosses an abandoned railroad line and passes homes, intersecting with DE 300 in the center of town.

Past Kenton, DE 42 continues to the east-southeast on Seven Hickories Road, running through farmland with woods and residences. In Seven Hickories, the route intersects DE 15 and the two routes head east for a concurrency. In Moores Corner, DE 15 splits from DE 42 by heading southeast on Kenton Road. DE 42 continues east-northeast through woodland and homes, passing to the south of Delaware Airpark. The route enters Cheswold, where it becomes Main Street. The road passes homes in the town, crossing Norfolk Southern's Delmarva Secondary railroad line. DE 42 runs past more residences and businesses before coming to an intersection with US 13 on the eastern edge of Cheswold.

After the US 13 intersection, the route continues northeast on Fast Landing Road. DE 42 passes over the DE 1 toll road, where it has ramps for emergency vehicles but no public access. The road heads through farmland with some woodland and residences, curving to the east. Farther east, the route turns southeast into marshland adjacent to the Leipsic River. DE 42 enters the town of Leipsic where it heads east on Second Street into residential areas and ends at DE 9.

DE 42 has an annual average daily traffic count ranging from a high of 8,800 vehicles at the Commerce Street intersection in Cheswold to a low of 516 vehicles at the eastern terminus at DE 9. None of DE 42 is part of the National Highway System.

By 1920, what is now DE 42 existed as an unimproved county road. The road was completed as a state highway between Kenton and Lepisic by 1924. By 1932, the route was under construction as a state highway between Blackiston and Kenton. When Delaware created its state highway system by 1936, DE 42 was assigned to its current alignment between DE 300 in Kenton and DE 9 in Leipsic and the state highway between Blackiston and Kenton was completed. By 1966, the route was extended to Blackiston.

The entire route is in Kent County.