Rehoboth Beach is a city on the Atlantic Ocean along the Delaware Beaches in eastern Sussex County, Delaware, United States. As of 2…Rehoboth Beach is a city on the Atlantic Ocean along the Delaware Beaches in eastern Sussex County, Delaware, United States. As of 2020, its population was 1,108. Along with the neighboring coastal town of Lewes, Rehoboth Beach is one of the principal cities of Delaware's rapidly growing Cape Region. Rehoboth Beach lies within the Salisbury metropolitan area.