Delaware Route 20 (DE 20) is an east–west state highway in Sussex County, Delaware. Its western terminus is the Maryland state line in Reliance, where the road continues as Maryland Route 392 (MD 392). Its eastern terminus is DE 54 west of Fenwick Island. The route runs through rural areas of Sussex County and passes through the towns of Seaford, Millsboro, and Dagsboro. DE 20 intersects U.S. Route 13 (US 13) in Seaford, US 9 in Hardscrabble, US 113 and DE 24 in Millsboro, DE 26 in Dagsboro, and DE 17 in Roxana. DE 20 was originally created by 1936 to run from the Maryland border east to US 113 in Millsboro. By 1970, it was realigned to bypass Seaford. The route was extended east to DE 1 in Fenwick Island by 1994; however, the eastern terminus was cut back to DE 54 in 2005 to avoid the concurrency with that route.

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.