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There are a number of areas in the eastern contiguous United States known informally as tri-state areas. Often, a tri-state area is a region associated with a particular town or metropolis that, with its adjacent suburbs, lies across three states. Some, but not all, of these involve a state boundary tripoint. Other "tri-state" areas have a more diffuse population that shares a connected economy and geography, especially with respect to geology, botany, or climate, such as the tri-state area of New York, New Jersey, and Connecticut. The use of the term "tri-state area" is often encountered in movies and radio and television commercials.
- The New York metropolitan area, which covers parts of the states of New York, New Jersey, and Connecticut.
- The Delaware Valley region, which includes eastern Pennsylvania, southern New Jersey, and northern Delaware.
- The Chicago tri-state area, also known as Chicagoland, which includes parts of Illinois, Indiana, and Wisconsin.
- The Greater Memphis area or Mid-South consisting of West Tennessee, North Mississippi, and the Arkansas delta.
- 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 colloquially referred to as "the DMV" (DC, Maryland, Virginia).
- The "Joplin District", a lead and zinc mining region of Oklahoma, Kansas, and Missouri, produces mineral specimens known as "tri-state" minerals, typically consisting mainly of sphalerite.
- The Illinois-Indiana-Kentucky Tri-State Area includes Evansville, Indiana and adjacent parts of Illinois and Kentucky.
- The Huntington-Ashland-Ironton metropolitan area incorporates towns in Kentucky, Ohio, and West Virginia.
The Quincy, Evansville, and Huntington-Ashland areas are noteworthy for the states included all being separated by rivers.
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), 34 are on dry land and 28 are in water.
|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||Marker on dry land at surface level and unmarked on lake in cavern directly below. Stolen in 2009 and returned two years later.|
|Arizona||Nevada||Utah||Marked with a red sandstone monument.|
|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||Missouri||Oklahoma||Marked with a stone monument.|
|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.|
|California||Nevada||Oregon||Marked with a cairn.|
|Colorado||Kansas||Nebraska||Marked with a brass disc.|
|Colorado||Kansas||Oklahoma||8 Mile Corner. Marker is concealed in crypt beneath removable manhole cover.|
|Colorado||Nebraska||Wyoming||Marked with a stone surrounded by a three-stone colored base.|
|Colorado||New Mexico||Oklahoma||Preston Monument|
|Connecticut||Massachusetts||New York||See Brace Mountain or Mount Frissell. Marked with a stone inscribed with MASS-1898-NY and sometimes a "scratched-on" CONN.|
|Connecticut||Massachusetts||Rhode Island||See Thompson, Connecticut. Marked with a stone inscribed with MASS-CONN-RI.|
|Delaware||Maryland||Pennsylvania||See Delaware Wedge. Marked with a stone inscribed with M-M-P-P as this was not intended to be the original tri-point.|
|Idaho||Montana||Wyoming||Located within Yellowstone National Park. Marked, although difficult to access.|
|Idaho||Nevada||Oregon||Marked with a three-sided stone inscribed with N-I-O on the respective faces.|
|Idaho||Nevada||Utah||Marked with a granite monument inscribed with the respective states' names.|
|Idaho||Utah||Wyoming||Marked with a stone.|
|Indiana||Michigan||Ohio||Brass marker with the shapes of the three states is located in a monument box beneath the surface of a rural road. Was set in 1999 and is referenced by a granite marker 20 feet to the east on the Michigan-Ohio line.|
|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 with a plaque on a seldom used dead-end road.|
|Kentucky||Tennessee||Virginia||Tri-State Peak Located within Cumberland Gap National Historical Park. Marked.|
|Kentucky||Virginia||West Virginia||Marked with a USGS marker on top of a two-foot high iron pipe at the river's high point.|
|Maryland||Pennsylvania||West Virginia||Marked with a pyramid-like stone.|
|Massachusetts||New Hampshire||Vermont||Marker is technically on dry land, but buried within river bed due to a dam's construction downstream.|
|Massachusetts||New York||Vermont||Marked with a stone.|
|Montana||North Dakota||South Dakota||Marked with a red granite stone.|
|Montana||South Dakota||Wyoming||Marked with a stone within a fence.|
|Nebraska||South Dakota||Wyoming||Marked with a stone within a fence.|
|New Mexico||Oklahoma||Texas||Texomex Marker|
Regions with no Tripoint
The following tri-state areas are also notable, but have no tripoint:
- Four Corners
- Four State Area
- Twin cities (geographical proximity), which includes tri-city
- Quad cities
- "Tri State Corners in the United States" (PDF). Jack Parsell.
- Wheatley, Thomas. "Camak Stone, border marker between Tennessee and Georgia, is missing". Creativve Loafing. Retrieved 7 May 2017.
- Vardeman, Johnny. "Stolen stone returns home minus fanfare". Gainesville Times. Retrieved 7 May 2017.
- http://www.bjbsoftware.com/corners/pointdetail.php3?point=12 AZ-NV-UT Corner
- http://www.bjbsoftware.com/corners/pointdetail.php3?point=6 AR-MO-OK Corner
- http://www.bjbsoftware.com/corners/docs/canvor.pdf CA-NV-OR Corner
- http://www.bjbsoftware.com/corners/docs/coksne.pdf CO-KS-NE Corner
- http://www.bjbsoftware.com/corners/docs/conewy.pdf CO-NE-WY Corner
- http://www.bjbsoftware.com/corners/docs/coutwy.pdf CO-UT-WY Corner
- http://www.bjbsoftware.com/corners/pointdetail.php3?point=19 CT-MA-NY Corner
- http://www.bjbsoftware.com/corners/pointdetail.php3?point=20 CT-MA-RI Corner
- http://www.bjbsoftware.com/corners/pointdetail.php3?point=24 DE-MD-PA Corner
- http://www.bjbsoftware.com/corners/docs/ganctn.pdf GA-NC-TN Corner
- http://www.bjbsoftware.com/corners/docs/idmtwy.pdf ID-MT-WY Corner
- http://www.bjbsoftware.com/corners/docs/idnvor.pdf ID-NV-OR Corner
- http://www.bjbsoftware.com/corners/docs/idnvut.pdf ID-NV-UT Corner
- http://www.bjbsoftware.com/corners/docs/idutwy.pdf ID-UT-WY Corner
- http://www.bjbsoftware.com/corners/docs/inmioh.pdf Jack Parsell's description of the IN-MI-OH tripoint
- Geocaching. "Geocaching - The Official Global GPS Cache Hunt Site".
- http://www.bjbsoftware.com/corners/photos/IAMNSDBrian.jpg Photo by Gregg A. Butler of the IA-MN-SD tripoint and its witness post
- http://www.bjbsoftware.com/corners/pointdetail.php3?point=46 KS-MO-OK Corner
- KY-TN-VA Tri-State Peak at Cumberland Gap National Historical Park
- http://www.bjbsoftware.com/corners/docs/kyvawv.pdf KY-VA-WV Corner
- http://www.bjbsoftware.com/corners/docs/mdpawv.pdf MD-PA-WV Corner
- Eric Jones. New Hampshire Curiosities. Globe Pequot, 2006. p114-5.
- http://www.bjbsoftware.com/corners/pointdetail.php3?point=54 MA-NY-VT Corner
- http://www.bjbsoftware.com/corners/docs/mtndsd.pdf MT-ND-SD Corner
- http://www.bjbsoftware.com/corners/docs/mtsdwy.pdf MT-SD-WY Corner
- http://www.bjbsoftware.com/corners/docs/nesdwy.pdf NE-SD-WY Corner
- http://www.bjbsoftware.com/corners/docs/nctnva.pdf NC-TN-VA Corner
- "Iowa - Minnesota - Wisconsin Tri-state".