Delaware Borders: States, Map & Complete Guide
Fact-checked • Updated January 11, 2026
Delaware borders two states: Pennsylvania to the north and Maryland to the west and south. The state also meets the Atlantic Ocean along its eastern coast and Delaware Bay to the northeast. Delaware's northern border with Pennsylvania includes the unique Twelve-Mile Circle, a rare circular border arc.
Delaware Border Map
Map showing Delaware's boundaries with Pennsylvania, Maryland, and surrounding water bodies.
Border Details
Explore each of Delaware's borders in detail. Click any card to learn more.
Pennsylvania
Delaware's northern border includes the unique Twelve-Mile Circle arc.
Maryland
Maryland borders Delaware on the west and south sides.
Atlantic Ocean
The Atlantic Ocean borders Delaware's eastern coast for about 28 miles.
Delaware Bay
Delaware Bay borders Delaware's northeastern coast.
Which States Border Delaware?
Delaware shares its borders with only two U.S. states: Pennsylvania to the north and Maryland to the west and south. This makes Delaware one of only a few states with just two neighbors, alongside Maine and South Carolina.
North: Pennsylvania (The Twelve-Mile Circle)
Pennsylvania and Delaware are separated by a border located on Delaware's northern edge. This boundary is unique because it includes the Twelve-Mile Circle, the only circular state border in the United States.
The Twelve-Mile Circle is an arc with a 12-mile radius centered on the New Castle Court House in New Castle, Delaware. This unusual border was established in colonial times and runs from the Delaware River in the east to the Maryland border in the west. New Castle County in Delaware is the only county that touches this border.
- Features the unique Twelve-Mile Circle arc
- Only circular state border in the U.S.
- 12-mile radius from New Castle Court House
West & South: Maryland
Maryland and Delaware are separated by a border that wraps around Delaware's western and southern sides. Maryland essentially surrounds Delaware on two sides, creating an unusual geographic relationship between the states.
The Delaware-Maryland border runs for about 125 miles total. The boundary includes both straight survey lines and the Transpeninsular Line. All three Delaware counties touch Maryland: New Castle in the north, Kent in the middle, and Sussex in the south. On the Maryland side, Cecil, Kent, Caroline, Dorchester, and Wicomico counties sit along the border.
- About 125 miles total border length
- Maryland wraps around Delaware's west and south
- All three Delaware counties touch Maryland
Water Borders: Atlantic Ocean & Delaware Bay
Delaware has coastline along both the Atlantic Ocean and Delaware Bay, giving the state important maritime access despite its small size.
East: Atlantic Ocean
The Atlantic Ocean borders Delaware's eastern coast for about 28 miles. This coastline runs from the Delaware Bay inlet in the north to the Maryland border in the south.
Delaware's Atlantic coast includes popular beach towns like Rehoboth Beach, Dewey Beach, Bethany Beach, and Fenwick Island. Sussex County contains the entire Atlantic coastline. The coast features sandy beaches and barrier islands that attract tourists throughout the year.
- About 28 miles of Atlantic coastline
- Popular beach towns: Rehoboth, Dewey, Bethany
- Sandy beaches and barrier islands
Northeast: Delaware Bay
Delaware Bay borders Delaware's northeastern coast, separating it from New Jersey across the water. The bay is actually the estuary of the Delaware River, which flows into the Atlantic Ocean.
Delaware Bay provides Delaware with important shipping access, with the Port of Wilmington serving as a major East Coast port. The bay coastline runs for about 50 miles along New Castle and Kent counties. While New Jersey sits across the bay, Delaware and New Jersey do not share a land border.
- About 50 miles of bay coastline
- Port of Wilmington on the bay
- Separates Delaware from New Jersey
The Twelve-Mile Circle: America's Only Circular Border
Delaware's northern border with Pennsylvania is one of the most unusual state borders in the United States. The Twelve-Mile Circle is a perfect arc with a 12-mile radius, centered on the cupola of the Old Court House in New Castle, Delaware. This border was established in 1701 and remains the only circular state boundary in the country. The circle was originally surveyed using a compass and chain, creating a geometric border that predates most other state boundaries by over a century.
Only Two Neighboring States
Delaware is one of only three states that border exactly two other states. The others are Maine (bordering only New Hampshire) and South Carolina (bordering only North Carolina and Georgia—wait, that's two). Delaware's small size and location on the Delmarva Peninsula limit its land borders to just Pennsylvania and Maryland, though it faces New Jersey across Delaware Bay.
Key Facts & Statistics
This table shows every border Delaware shares, organized by direction and type.
Delaware borders exactly two U.S. states: Pennsylvania and Maryland
Frequently Asked Questions
What borders Delaware?
What state borders Delaware?
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Does Delaware border New Jersey?
What is the Twelve-Mile Circle?
Sources & References
This article has been researched using authoritative sources to ensure accuracy and reliability.
Historical information about the Twelve-Mile Circle boundary