There are a number of areas in the 48 contiguous United States known informally as tri-state areas. Often, 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. Other "tri-state" areas have a more diffuse population that shares a connected economy and geography, especially with respect to climate, such as the tri-state area of Indiana, Ohio and Michigan.

The most frequently referenced tri-state area is that which refers with the New York metropolitan area, which covers parts of the states of New York, New Jersey and Connecticut. It is often referenced in New York radio, as well as through countless television commercials.

The Delaware Valley region, which includes eastern Pennsylvania, southern New Jersey, and northern Delaware, is also frequently referred to as a tri-state area in radio and TV advertising in the Philadelphia market.

Four 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; the Chicago tri-state area, also known as Chicagoland, which includes parts of Illinois, Indiana, and Wisconsin; and the Greater Memphis area or Mid-South consisting of West Tennessee, North Mississippi, and the Arkansas delta.

The New York metropolitan area includes the most populous city in the United States (New York City); Long Island and the Mid- and Lower Hudson Valley in the state of New York; the five largest cities in New Jersey (Newark, Jersey City, Paterson, Elizabeth, and Edison) and their vicinities; six of the seven largest cities in Connecticut (Bridgeport (the largest city in Connecticut), New Haven, Stamford, Waterbury, Norwalk, and Danbury) and their vicinities; and five counties in northeastern Pennsylvania.

As per the 2013 United States Census Bureau estimates, the New York metropolitan area remains by a significant margin the most populous in the United States, as defined by both the Metropolitan Statistical Area (20.1 million residents) and the Combined Statistical Area (23.6 million residents); it is also one of the most populous urban agglomerations in the world, and the single largest in North America. The New York metropolitan area continues to be, by far, the premier gateway for legal immigration to the United States. The MSA covers 6,720 sq mi (17,405 km²), while the CSA area is 13,318 sq mi (34,493 km²), encompassing an ethnically and geographically diverse region. The New York metropolitan area's population is larger than that of the state of New York.