Delaware lies entirely within the Atlantic Coastal Plain except for its northern tip, above the Christina River, which is part of the Piedmont Plateau. The state's highest elevation is 448 ft (137 m) on Ebright Road, near Centerville, New Castle County. The rolling hills and pastures of the north give way to marshy regions in the south (notably Cypress Swamp), with sandy beaches along the coast. Delaware's mean elevation, 60 ft (18 m), is the lowest in the US.

Of all Delaware's rivers, only the Nanticoke, Choptank, and Pocomoke flow westward into Chesapeake Bay. The remainder—including the Christina, Appoquinimink, Leipsic, St. Jones, Murderkill, Mispillion, Broadkill, and Indian—flow into Delaware Bay. There are dozens of inland freshwater lakes and ponds.