List of river borders of U.S. states

Because of its unique history, many of the boundaries of the political divisions of the United States were artificially constructed (rather than being permitted to evolve and drawn using natural features of the landscape). Therefore, many U.S. states have straight lines as boundaries, especially in the West. However, there are a number of states, particularly in the Midwest, North and South with at least partial river borders.

Map of US river/waterway state borders(highlighted).

The rule of the thread of the channel and its exceptionsEdit

Typically the boundary is the "thread of the channel", under a rule that the United States inherited from England, where it applies to boundaries between counties.[citation needed] There are at least six exceptions, where the boundary is one bank of the river rather than the thread of the channel:

  • The boundary between New Hampshire and Vermont is the west bank of the Connecticut River. This was established as the eastern boundary of New York by a grant of King Charles II in 1664. It was disregarded by Governor Benning Wentworth of New Hampshire, who treated the New Hampshire Grants west of the river as a de facto part of New Hampshire during the years 1649–1764, but King George III put an end to that in 1764. In August 1781 the Continental Congress decided it would recognize the then largely unrecognized state of Vermont, which had been organized in defiance of New York, on condition that Vermont would agree to certain boundaries. In 1782, the legislature of Vermont agreed, but nonetheless Vermont was not admitted to the Union until 1791. In 1933, citing the 1782 legislation, the United States Supreme Court denied the petition from the state of Vermont to make the boundary the thread of the channel.
  • The boundary between Kentucky and West Virginia and the three states to their north – Ohio, Indiana, and Illinois – is based on a historical northern bank of the Ohio River.[1] In 1763, Britain defeated France in the Seven Years' War, whose North American theater was called the French and Indian War. At that time Canada, which had been a French colony, became a British colony, and Parliament made the north bank of the Ohio the southern boundary of Canada. The river was thus included in the district of Kentucky, which was then a part of Virginia.[citation needed] In January 1980, the U.S. Supreme Court ruled in Ohio v. Kentucky that the state line is the low-water mark of the Ohio River's north shore as of Kentucky's admission to the Union in 1792.[2] Because both damming and natural changes have rendered the 1792 shore virtually undetectable in many places, the exact boundary was decided in the 1990s in settlements among the states.[3]
  • The boundary between Delaware and New Jersey north of 39° 30' north latitude is the east bank of the Delaware River.[citation needed]
  • The boundary between Delaware and New Jersey, south of a certain point, is the west bank of the Delaware River rather than the thread of the channel.
  • The boundary between Maryland and Virginia is the south bank of the Potomac River. This also applies both to the border between Maryland and West Virginia (from Harper's Ferry to the source of the Potomac near the Fairfax Stone) since the latter was at one point part of Virginia, and to the border between Virginia and Washington, D.C. since the capital was established from a section of Maryland property.
  • The boundary between Alabama and Georgia, south of West Point, Georgia, is the west bank of the Chattahoochee at the mean water mark. This was established in the 1860 Supreme Court ruling Alabama v. Georgia.

List of river bordersEdit

The course of the Charles River was used to indirectly define the border between Massachusetts and Rhode Island. The Merrimack River defines part of the border between Massachusetts and New Hampshire, which runs parallel to the river, three miles north of it (see Northern boundary of Massachusetts.)


  1. ^ Zimmerman, Joseph Francis (2007). Interstate Disputes: The Supreme Court's Original Jurisdiction. p. 74.
  2. ^ "Kentucky, Indiana and Ohio End River Boundary Dispute". The New York Times. Associated Press. October 21, 1981.
  3. ^ Campbell, Linda P.; Crimmins, Jerry (May 29, 1991). "High Court Gives Illinois a Piece of Ohio River". Chicago Tribune.