The boundaries of a CDP have no legal status. Thus, they 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), 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.