There are a number of areas in the 48 contiguous United States known informally as tri-state areas. A tri-state area is an area associated with a particular town or metropolis that lies across three states. Some, but not all, of these involve a state boundary tripoint.
Three other prominent areas that have been labeled tri-state areas are the Cincinnati tri-state area, including Ohio, Kentucky, and Indiana; the Pittsburgh tri-state area, covering parts of Pennsylvania, Ohio, and West Virginia; and the Chicago tri-state area, also known as Chicagoland, which includes Illinois, Indiana, and Wisconsin.
Smaller tri-state areas include those of Dubuque, Iowa, which spills over into Illinois and Wisconsin; of Quincy, Illinois, which includes parts of Missouri and Iowa; Evansville, Indiana, which includes parts of Illinois and Kentucky; the Chattanooga, Tennessee tri-state area which includes Alabama and Georgia; and the Huntington (W.V.)-Ashland (Ky.)-Ironton (Oh.) Tri-State region, which incorporates areas of Kentucky, Ohio, and West Virginia. The Quincy, Evansville, and Huntington-Ashland areas are noteworthy for the states included all being separated by rivers.
The area that includes Washington, D.C. and the nearby parts of Maryland and the Virginias is sometimes loosely referred to as a "tri-state area," although the District of Columbia is not a state; however, with the presence of Jefferson County, West Virginia in the official Washington–Arlington–Alexandria Metropolitan Statistical Area, the region, as defined by the US Government, does in fact include three states. This area is more commonly/colloquially referred to as the "DMV" (DC, Maryland, Virginia).
The term Tri-state area is used often in the children's television program Phineas and Ferb. The evil Dr. Doofenshmirtz makes reference in every episode to wanting to take over the tri-state area.
Land tripoints 
Of the 62 points in the United States where three and only three states meet (each of which may be associated with its own tri-state area), 35 are on dry land. They are:
|State 1||State 2||State 3||Notes|
|Alabama||Florida||Georgia||Marker on riverbank is actually a few feet above and west of true tripoint at high-water line.|
|Alabama||Georgia||Tennessee||Recently stolen marker on dry land at surface level and unmarked on lake in cavern directly below.|
|Arkansas||Louisiana||Mississippi||Unmarked on silt island in river connected to west bank by riprap.|
|Arkansas||Louisiana||Texas||See Ark-La-Tex. Marker in process of being surrounded and absorbed by tree.|
|Arkansas||Oklahoma||Texas||Unmarked on seasonal silt island or in river bed, but Oklahoma-Texas state line as revised in 2000 is defective in not extending from vegetation line on south bank to pre-established tripoint.|
|Colorado||Kansas||Oklahoma||8 Mile Corner. Marker is concealed in crypt beneath removable manhole cover.|
|Colorado||New Mexico||Oklahoma||Preston Monument|
|Connecticut||Massachusetts||New York||See Brace Mountain or Mount Frissell. Marked.|
|Connecticut||Massachusetts||Rhode Island||See Thompson, Connecticut. Marked.|
|Delaware||Maryland||Pennsylvania||See Delaware Wedge. Marked.|
|Idaho||Montana||Wyoming||Located within Yellowstone National Park. Marked.|
|Indiana||Michigan||Ohio||Marker is located in a crypt beneath the surface of a rural road. Was set in 1999and used to have a removable metal plate protecting it, but it has been missing since fall 2010.|
|Iowa||Minnesota||South Dakota||True point is marked with a disc in the center of a T-shaped road intersection. A witness monument nearby in the South Dakota corner acknowledges the tri-point being set in 1859.|
|Kansas||Missouri||Oklahoma||Marked. On seldom used dead-end road. Apparently a teenagers' backwoods drinking spot.|
|Kentucky||Tennessee||Virginia||Tri-State Peak Located within Cumberland Gap National Historical Park. Marked.|
|Massachusetts||New Hampshire||Vermont||Marker is technically on dry land, but buried within river bed.|
|Montana||North Dakota||South Dakota||Marked.|
|New Jersey||New York||Pennsylvania||Marked by the Tri-State Monument in Port Jervis, New York by the confluence of the Delaware and Neversink Rivers.|
|New Mexico||Oklahoma||Texas||Texomex Marker|
Water tripoints 
Twenty-seven tripoints are under water:
Regions with no Tripoint 
The following tri-state areas are also notable, but have no tripoint:
See also 
- Four Corners
- Four State Area
- Phineas and Ferb (the series' setting in an undefined tri-state area is mentioned in every episode)
- Twin cities (geographical proximity), which includes tri-city
- "Tri State Corners in the United States". Jack Parsell.
- http://www.bjbsoftware.com/corners/docs/inmioh.pdf Jack Parsell's description of the tripoint
- http://www.bjbsoftware.com/corners/photos/IAMNSDBrian.jpg Photo by Gregg A. Butler of the IA-MN-SD tripoint and its witness post
- Tri-State Peak at Cumberland Gap National Historical Park
- Eric Jones. New Hampshire Curiosities. Globe Pequot, 2006. p114-5.