Because of its unique history, many of the boundaries of the political divisions of the United States were artificially constructed (rather than 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 many partial state boundaries, particularly in the

Midwest The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four Census Bureau Region, census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of ...

Northeast The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each se ...

, and

South South is one of the cardinal directions or Points of the compass, compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pro ...

, that are defined by rivers; in fact, only five states (Colorado, Hawaii, Montana, Utah, and Wyoming) completely lack any borders defined by rivers or waterways.

The rule of the thread of the channel and its exceptions

River boundaries are typically defined by the "thread of the channel" (the river's thalweg, usually in the approximate middle of the river's channel), under a rule that the United States inherited from England, where it applies to boundaries between counties. In the United States, there are at least six exceptions, however, 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 The Connecticut River is the longest river in the New England region of the United States, flowing roughly southward for through four states. It rises 300 yards (270 m) south of the U.S. border with Quebec, Canada, and discharges at Long Island ...

. This was established as the eastern boundary of

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

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 The Continental Congress was a series of legislative bodies, with some executive function, for thirteen of Britain's colonies in North America, and the newly declared United States just before, during, and after the American Revolutionary War. ...

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 boundaries between Kentucky and West Virginia and the three states to their north – Ohio, Indiana, and Illinois – is based on the historical northern bank of the

Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...

. 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. 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. 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. * The boundary between Delaware and New Jersey north of 39° 30' north latitude is the east bank of the

Delaware River The Delaware River is a major river in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. From the meeting of its branches in Hancock (village), New York, Hancock, New York, the river flows for along the borders of N ...

. * 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 Fairfax Stone Historical Monument State Park is a West Virginia state park commemorating the Fairfax Stone, a surveyor's marker and boundary stone at the source of the North Branch of the Potomac River. The original stone was placed on October ...

) 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 River The Chattahoochee River forms the southern half of the Alabama and Georgia border, as well as a portion of the Florida - Georgia border. It is a tributary of the Apalachicola River, a relatively short river formed by the confluence of the Chatta ...

at the mean water mark. This was established in an 1860 Supreme Court ruling, '' Alabama v. Georgia''.

List of river borders

Arthur Kill The Arthur Kill (sometimes referred to as the Staten Island Sound) is a tidal strait between Staten Island (also known as Richmond County), New York and Union and Middlesex counties, New Jersey. It is a major navigational channel of the Port of ...

: New Jersey,

( tidal strait) * Big Sandy River: Kentucky, West Virginia * Big Sioux River: South Dakota, Iowa * Blackwater River: Virginia, North Carolina *

Bois de Sioux River The Bois de Sioux River () drains Lake Traverse, the southernmost body of water in the Hudson Bay watershed of North America. It is a tributary of the Red River of the North and defines part of the western border of the U.S. state of Minnesota, ...

: South Dakota, Minnesota, North Dakota * Brule River: Michigan, Wisconsin * Byram River: Connecticut, New York * Catawba River: North Carolina, South Carolina *

: Alabama, Florida, Georgia * Chattooga River: Georgia, South Carolina * Colorado River: Arizona, Nevada, California, Baja California *

Columbia River The Columbia River (Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, C ...

: Washington, Oregon *

: New Hampshire, Vermont *

: New York, Pennsylvania, New Jersey, Delaware * Des Moines River: Iowa, Missouri * Detroit River: Michigan, Ontario * Great Miami River (mouth only): Ohio, Indiana *

Halls Stream Halls Stream or Rivière Hall is a tributary of the Connecticut River in eastern North America. For most of its length, it forms the Canada–United States border, with the province of Quebec (Canada) to its west and the state of New Hampshire ...

: New Hampshire, Quebec * Hudson River (lower part only): New Jersey, New York *

Kill Van Kull __NOTOC__ The Kill Van Kull is a tidal strait between Staten Island, New York and Bayonne, New Jersey in the United States. It is approximately long and wide and connects Newark Bay with Upper New York Bay. The Robbins Reef Light marks the ...

: New Jersey, New York (tidal strait) * Menominee River: Michigan, Wisconsin * Mississippi River: Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana * Missouri River: South Dakota, Nebraska, Iowa, Missouri, Kansas * Montreal River: Michigan ( Upper Peninsula), Wisconsin *

Niagara River The Niagara River () is a river that flows north from Lake Erie to Lake Ontario. It forms part of the border between the province of Ontario in Canada (on the west) and the state of New York (state), New York in the United States (on the east) ...

: New York, Ontario *

: Illinois, Indiana, Ohio, Kentucky, West Virginia *

Palmer River The Palmer River is a river located in Far North Queensland, Australia. The area surrounding the river was the site of a gold rush in the late 19th century which started in 1873. Course and features The headwaters of the Palmer River rise in ...

: Rhode Island, Massachusetts *

Pawcatuck River The Pawcatuck River is a river in the US states of Rhode Island and Connecticut flowing approximately .U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed April 1, 2011 There are eight dam ...

: Connecticut, Rhode Island * Pearl River: Mississippi, Louisiana * Perdido River: Florida, Alabama * Pigeon River: Minnesota, Ontario * Pine River: Minnesota, Ontario * Piscataqua River: Maine, New Hampshire *

Pocomoke River The Pocomoke River stretches approximately U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed April 1, 2011 from southern Delaware through southeastern Maryland in the United States. At it ...

: Maryland, Virginia * Poteau River: Arkansas, Oklahoma * Potomac River: Maryland, Virginia, D.C., West Virginia *

Poultney River The Poultney River is a river in southwestern Vermont and eastern New York. In its 40-mile long course, the river drains approximately 263 square miles as it flows northwards into the southern end of Lake Champlain. Course The Poultney River's ...

: Vermont, New York * Rainy River: Minnesota, Ontario * Red River of the North: North Dakota, Minnesota *

Red River of the South The Red River, or sometimes the Red River of the South, is a major river in the Southern United States. It was named for its reddish water color from passing through red-bed country in its watershed. It is one of several rivers with that name ...

: Texas, Oklahoma, Arkansas *

Rio Grande The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio G ...

: New Mexico, Texas,

Chihuahua Chihuahua may refer to: Places *Chihuahua (state), a Mexican state **Chihuahua (dog), a breed of dog named after the state **Chihuahua cheese, a type of cheese originating in the state **Chihuahua City, the capital city of the state **Chihuahua Mun ...

Coahuila Coahuila (), formally Coahuila de Zaragoza (), officially the Free and Sovereign State of Coahuila de Zaragoza ( es, Estado Libre y Soberano de Coahuila de Zaragoza), is one of the 32 states of Mexico. Coahuila borders the Mexican states of N ...

Nuevo León Nuevo León () is a state in the northeast region of Mexico. The state was named after the New Kingdom of León, an administrative territory from the Viceroyalty of New Spain, itself was named after the historic Spanish Kingdom of León. With a ...

, Tamaulipas *

Runnins River The Runnins River is a river in the U.S. states of Massachusetts and Rhode Island. It flows approximately 14 km (9 mi). Course The river begins in Seekonk, Massachusetts in the swamps east of Prospect Street, near Walker Street. From the ...

: Rhode Island, Massachusetts * Sabine River: Texas, Louisiana * St. Clair River: Michigan, Ontario *

St. Croix River (Maine-New Brunswick) The St. Croix River is any of several rivers in North America: * St. Croix River (Maine–New Brunswick) The St. Croix River (french: Fleuve Sainte-Croix; Malecite-Passamaquoddy language, Maliseet-Passamaquoddy: ''Skutik'') is a river in northe ...

: Maine, New Brunswick *

St. Croix River (Wisconsin-Minnesota) The St. Croix River is any of several rivers in North America: * St. Croix River (Maine–New Brunswick) The St. Croix River (french: Fleuve Sainte-Croix; Malecite-Passamaquoddy language, Maliseet-Passamaquoddy: ''Skutik'') is a river in northe ...

: Minnesota, Wisconsin * St. Francis River (Missouri-Arkansas): Arkansas, Missouri * St. Francis River (Quebec-Maine): Maine, Quebec * St. John River: Maine, New Brunswick * St. Lawrence River: New York, Ontario *

St. Louis River The Saint Louis River (abbreviated St. Louis River) is a river in the U.S. states of Minnesota and Wisconsin that flows into Lake Superior. The largest U.S. river to flow into the lake, it is in lengthU.S. Geological Survey. National Hydrograph ...

: Minnesota, Wisconsin *

St. Marys River (Florida-Georgia) The St. Marys River, St. Mary's River, or St. Mary River may refer to: Canada * St. Mary River (British Columbia), tributary of the Kootenay River * St. Mary's River (Nova Scotia), an important Nova Scotia salmon river United States * St. Marys R ...

: Florida, Georgia *

St. Marys River (Michigan-Ontario) The St. Marys River, St. Mary's River, or St. Mary River may refer to: Canada * St. Mary River (British Columbia), tributary of the Kootenay River * St. Mary's River (Nova Scotia), an important Nova Scotia salmon river United States * St. Marys R ...

: Michigan, Ontario *

Salmon Falls River The Salmon Falls River is a tributary of the Piscataqua River in the U.S. states of Maine and New Hampshire. It rises at Great East Lake, Newichawannock Canal, and Horn Pond and flows south-southeast for approximately , forming the border between ...

: New Hampshire, Maine *

Savannah River The Savannah River is a major river in the southeastern United States, forming most of the border between the states of South Carolina and Georgia. Two tributaries of the Savannah, the Tugaloo River and the Chattooga River, form the norther ...

: South Carolina, Georgia *

Snake River The Snake River is a major river of the greater Pacific Northwest region in the United States. At long, it is the largest tributary of the Columbia River, in turn, the largest North American river that empties into the Pacific Ocean. The Snake ...

: Idaho, Washington, Oregon * Tennessee River: Kentucky, Tennessee, Mississippi, Alabama * Tug Fork River: Kentucky, West Virginia, Virginia * Tugaloo River: Georgia, South Carolina * Wabash River: Illinois, Indiana 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.)

References

{{DEFAULTSORT:River Borders Of U.S. States Geography of the United States * Borders of U.S. states