Delaware - Geography

Geography

Main articles: Twelve-Mile Circle, Wedge (border), Mason–Dixon Line, and Transpeninsular Line See also: "Counties" section below

Delaware is 96 miles (154 km) long and ranges from 9 miles (14 km) to 35 miles (56 km) across, totaling 1,954 square miles (5,060 km2), making it the second-smallest state in the United States after Rhode Island. Delaware is bounded to the north by Pennsylvania; to the east by the Delaware River, Delaware Bay, New Jersey and the Atlantic Ocean; and to the west and south by Maryland. Small portions of Delaware are also situated on the eastern side of the Delaware River sharing land boundaries with New Jersey. The state of Delaware, together with the Eastern Shore counties of Maryland and two counties of Virginia, form the Delmarva Peninsula, which stretches down the Mid-Atlantic Coast.

The definition of the northern boundary of the state is unusual. Most of the boundary between Delaware and Pennsylvania was originally defined by an arc extending 12 miles (19.3 km) from the cupola of the courthouse in the city of New Castle. This boundary is often referred to as the Twelve-Mile Circle. This is the only nominally circular state boundary in the United States.

This border extends all the way east to the low-tide mark on the New Jersey shore, then continues south along the shoreline until it again reaches the 12-mile (19 km) arc in the south; then the boundary continues in a more conventional way in the middle of the main channel (thalweg) of the Delaware River. To the west, a portion of the arc extends past the easternmost edge of Maryland. The remaining western border runs slightly east of due south from its intersection with the arc. The Wedge of land between the northwest part of the arc and the Maryland border was claimed by both Delaware and Pennsylvania until 1921, when Delaware's claim was confirmed.