The Delaware River is a major river in the Mid-Atlantic region of the United States and is the longest free-flowing (undammed) river in the Eastern United States. From the meeting of its branches in Hancock, New York, the river flows for 282 miles (454 km) along the borders of New York, Pennsylvania, New Jersey, and Delaware, before emptying into Delaware Bay.

The Mid-Atlantic is a region of the United States located in the overlap between the Northeastern and Southeastern states of the United States. Its exact definition differs upon source, but the region typically includes Delaware, the District of Columbia, Maryland, New Jersey, New York, Pennsylvania, Virginia, and West Virginia with other sources including or excluding other states or areas in the Northeast and Southeast. The region has its origin in the Middle Colonies of the 18th century, its states being among the Thirteen Colonies of pre-revolutionary British America. As of the 2020 census, the region had a population of 60,783,913, representing slightly over 18% of the nation's population.