Geographically there has always been some debate as to where the Northeastern United States begins and ends. The vast area from central Virginia to northern Maine, and from western Pennsylvania (Pittsburgh) to the Atlantic Ocean, have all been loosely grouped into the Northeast at one time or another. Much of the debate has been what the cultural, economic, and urban aspects of the Northeast are, and where they begin or end as one reaches the borders of the region.
Using the Census Bureau's definition of the Northeast, the region includes nine states: they are Maine, New York, New Jersey, Vermont, Massachusetts, Rhode Island, Connecticut, New Hampshire, and Pennsylvania.[a] The region is often subdivided into New England (the six states east of New York) and the Mid-Atlantic states (New York, New Jersey, and Pennsylvania). This definition has been essentially unchanged since 1880 and is widely used as a standard for data tabulation. However, the Census Bureau has acknowledged the obvious limitations of this definition and the potential merits of a proposal created after the 1950 census that would include changing regional boundaries to include Delaware, Maryland, and the District of Columbia, with the Mid-Atlantic states, but ultimately decided that "the new system did not win enough overall acceptance among data users to warrant adoption as an official new set of general-purpose State groupings. The previous development of many series of statistics, arranged and issued over long periods of time on the basis of the existing State groupings, favored the retention of the summary units of the current regions and divisions." The Census Bureau confirmed in 1994 that it would continue to "review the components of the regions and divisions to ensure that they continue to represent the most useful combinations of States and State equivalents."
Many organizations and reference works follow the Census Bureau's definition for the region; however, other entities define the Northeastern United States in significantly different ways for various purposes. The Association of American Geographers divides the Northeast into two divisions: "New England", which consists of Maine, Vermont, New Hampshire, Massachusetts, Rhode Island, and Connecticut; and the "Middle States", which consists of New York, Pennsylvania, New Jersey, and Delaware. Similarly, the Geological Society of America defines the Northeast as these same states but with the addition of Maryland and the District of Columbia. The narrowest definitions include only the states of New England. Other more restrictive definitions include New England and New York as part of the Northeast United States, but exclude Pennsylvania and New Jersey.
States beyond the Census Bureau definition are included in Northeast Region by various other entities:
- Various organizations include: Delaware, Maryland, and District of Columbia.
- The US EPA and NOAA include in their Northeast Region: Delaware, Maryland, and West Virginia.
- The National Fish and Wildlife Service includes in their Northeast Region: Delaware, Maryland, District of Columbia, West Virginia, and Virginia.
- The National Park Service includes in their Northeast Region: Delaware, Maryland, West Virginia, and Virginia (though small parts are also in the National Capital Region).