A census-designated place (CDP) is a concentration of population defined by the United States Census Bureau for statistical purposes only. CDPs have been used in each decennial census since 1980 as the counterparts of incorporated places, such as self-governing cities, towns, and villages, for the purposes of gathering and correlating statistical data. CDPs are populated areas that generally include one officially designated but currently unincorporated community, for which the CDP is named, plus surrounding inhabited countryside of varying dimensions and, occasionally, other, smaller unincorporated communities as well. CDPs include small rural communities, colonias located along the Mexico–United States border, and unincorporated resort and retirement communities and their environs.
The boundaries of a CDP have no legal status and may not always correspond with the local understanding of the area or community with the same name. However, criteria established for the 2010 Census require that a CDP name "be one that is recognized and used in daily communication by the residents of the community" (not "a name developed solely for planning or other purposes") and recommend that a CDP's boundaries be mapped based on the geographic extent associated with inhabitants' regular use of the named place.
The Census Bureau states that census-designated places are not considered incorporated places and that it includes only census-designated places in its city population list for Hawaii because that state has no incorporated cities. In addition, census city lists from 2007 included Arlington County, Virginia's CDP in the list with the incorporated places, but since 2010, only the Urban Honolulu CDP, Hawaii, representing the historic core of Honolulu, Hawaii, is shown in the city and town estimates.
The Census Bureau reported data for some unincorporated places as early as the first census, the 1790 Census (for example, Louisville, Kentucky, which was not legally incorporated in Kentucky until 1828), though usage continued to develop through the 1890 Census, in which, the Census mixed unincorporated places with incorporated places in its products with "town" or "village" as its label. This made it confusing to determine which of the "towns" were or were not incorporated.
For the 1940 Census, the Census Bureau compiled a separate report of unofficial, unincorporated communities of 500 or more people. The Census Bureau officially defined this category as "unincorporated places" in the 1950 Census and used that term through the 1970 Census. For the 1950 Census, these types of places were identified only outside "urbanized areas". In 1960, the Census Bureau also identified unincorporated places inside urbanized areas (except in New England, whose political geography is based on the New England town, and is distinctly different from other areas of the U.S.), but with a population of at least 10,000. For the 1970 Census, the population threshold for "unincorporated places" in urbanized areas was reduced to 5,000.
For the 1980 Census, the designation was changed to "census designated places" and the designation was made available for places inside urbanized areas in New England. For the 1990 Census, the population threshold for CDPs in urbanized areas was reduced to 2,500. From 1950 through 1990, the Census Bureau specified other population requirements for unincorporated places or CDPs in Alaska, Puerto Rico, island areas, and Native American reservations. Minimum population criteria for CDPs were dropped with the 2000 Census.
The Census Bureau's Participant Statistical Areas Program (PSAP) allows designated participants to review and suggest modifications to the boundaries for CDPs. The PSAP was to be offered to county and municipal planning agencies during 2008.
The boundaries of such places may be defined in cooperation with local or tribal officials, but are not fixed, and do not affect the status of local government or incorporation; the territories thus defined are strictly statistical entities. CDP boundaries may change from one census to the next to reflect changes in settlement patterns. Further, as statistical entities, the boundaries of the CDP may not correspond with local understanding of the area with the same name. Recognized communities may be divided into two or more CDPs while on the other hand, two or more communities may be combined into one CDP. A CDP may also cover the unincorporated part of a named community where the rest lies within an incorporated place.
By defining an area as a CDP, that locality then appears in the same category of census data as incorporated places. This distinguishes CDPs from other census classifications, such as minor civil divisions (MCDs), which are in a separate category.
The population and demographics of the CDP are included in the data of county subdivisions containing the CDP. Generally, a CDP shall not be defined within the boundaries of what the Census Bureau regards to be an incorporated city, village or borough. However, the Census Bureau considers some towns in New England states, New Jersey and New York as well as townships in some other states as MCDs, even though they are incorporated municipalities in those states. In such states, CDPs may be defined within such towns or spanning the boundaries of multiple towns.
There are a number of reasons for the CDP designation: