List of river borders of U.S. states
Because of its unique history, many of the boundaries of 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. That said, there are a number of states, particularly in the Midwest, North and South with at least partial river borders.
- Arkansas River: Oklahoma, Arkansas
- Arthur Kill: New Jersey, New York (Tidal strait)
- Big Sandy River: Kentucky, West Virginia
- Big Sioux River: South Dakota, Iowa
- Blackwater River: Virginia, North Carolina
- Bois de Sioux River: South Dakota, Minnesota, North Dakota
- Brule River: Michigan, Wisconsin
- Byram River: Connecticut, New York
- Catawba River: North Carolina, South Carolina
- Chattahoochee River: Alabama, Georgia
- Chattooga River: Georgia, South Carolina
- Colorado River: Arizona, Nevada, California
- Columbia River: Washington, Oregon
- Connecticut River: New Hampshire, Vermont
- Delaware River: New York, Pennsylvania, New Jersey, Delaware
- Des Moines River: Iowa, Missouri
- Detroit River: Michigan, Ontario
- Great Miami River (mouth only): Ohio, Indiana
- Halls Stream: New Hampshire, Canada
- Hudson River (lower part only): New Jersey, New York
- Kill Van Kull: 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
- Monument Creek: Maine, New Brunswick
- Niagara River: New York, Ontario
- Ohio River: Illinois, Indiana, Ohio, Kentucky, West Virginia
- Palmer River: Rhode Island, Massachusetts
- Pawcatuck River: Connecticut, Rhode Island
- Pearl River: Mississippi, Louisiana
- Perdido River: Florida, Alabama
- Pigeon River: Minnesota, Ontario
- Piscataqua River: Maine, New Hampshire
- Pocomoke River: Maryland, Virginia
- Poteau River: Arkansas, Oklahoma
- Potomac River: Maryland, Virginia, Washington, D.C., West Virginia
- Poultney River: Vermont, New York
- Rainy River: Minnesota, Ontario, Canada
- Red River of the North: North Dakota, Minnesota
- Red River (Mississippi watershed): Texas, Oklahoma, Arkansas
- Rio Grande: New Mexico, Texas, Mexico
- Runnins River: Rhode Island, Massachusetts
- Sabine River: Texas-Louisiana
- St. Clair River: Michigan, Ontario
- St. Croix River (Maine-New Brunswick): Maine, New Brunswick
- St. Croix River (Wisconsin-Minnesota): Minnesota, Wisconsin
- St. Francis River (Missouri-Arkansas): Arkansas, Missouri
- St. Francis River (Quebec-Maine): Maine, Quebec
- St. John River: Maine, Quebec
- St. Lawrence River: New York, Ontario
- St. Louis River: Minnesota, Wisconsin
- St. Marys River (Florida-Georgia): Florida, Georgia
- St. Marys River (Michigan-Ontario): Michigan, Ontario
- Salmon Falls River: New Hampshire, Maine
- Savannah River: South Carolina, Georgia
- Snake River: 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 Merrimac River defines part of the border between Massachusetts and New Hampshire, but is offset three miles inside Massachusetts.