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 permitted to evolve and drawn using natural features of the landscape).

However, there are many partial state boundaries, particularly in the Midwest, Northeast, and South, that are defined by rivers; in fact, only four mainland states (Colorado, Montana, Utah, and Wyoming) completely lack any borders defined by rivers or waterways, as well as Hawaii whose borders are the islands.

[citation needed] 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 course of the Charles River was used to indirectly define the border between Massachusetts and Rhode Island.

[citation needed] 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.)

Nearly every US states' border has some portion that is a river or other water way; 44 in total.