The Census Bureau reported data for some unincorporated places as early as the first census in 1790 (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.10 This made it confusing to determine which of the "towns" were or were not incorporated.11
The 1900 through 1930 censuses did not report data for unincorporated places.12
For the 1940 census, the Census Bureau compiled a separate report of unofficial, unincorporated communities of 500 or more people.13 The Census Bureau officially defined this category as "unincorporated places" in the 1950 census and used that term through the 1970 census.14 For the 1950 census, these types of places were identified only outside "urbanized areas".15 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 10,000.16 For the 1970 census, the population threshold for "unincorporated places" in urbanized areas was reduced to 5,000.17
For the 1980 census, the designation was changed to "census designated places"18 and the designation was made available for places inside urbanized areas in New England.19 For the 1990 census, the population threshold for CDPs in urbanized areas was reduced to 2,500.20 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.2122
The Census Bureau's Participant Statistical Areas Program (PSAP) allows designated participants to review and suggest modifications to the boundaries for CDPs.23 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.2425 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.26
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.27 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.28
There are a number of reasons for the CDP designation:
"Geographic Terms and Concepts – Place". United States Census Bureau. December 6, 2012. Archived from the original on December 21, 2014. Retrieved December 11, 2014. https://web.archive.org/web/20141221174415/https://www.census.gov/geo/reference/gtc/gtc_place.html ↩
"Chapter 9 – Places" in Geographic Areas Reference Manual, United States Census Bureau. Accessed November 19, 2016. https://www2.census.gov/geo/pdfs/reference/GARM/Ch9GARM.pdf ↩
U.S. Bureau of the Census, "Census Designated Place (CDP) Program for the 2010 Census — Proposed Criteria", 72 Federal Register 17326-17329, April 6, 2007. http://edocket.access.gpo.gov/2007/pdf/E7-6465.pdf ↩
"Glossary". American FactFinder. U.S. Census Bureau. Archived from the original on February 8, 2015. Retrieved December 11, 2014. https://web.archive.org/web/20150208124000/http://factfinder.census.gov/help/en/index.htm#glossary.htm ↩
"Census Designated Place (CDP) Program for the 2010 Census – Final Criteria" (PDF). Federal Register (Volume 73, Number 30). February 13, 2008. Retrieved March 31, 2016. https://www.gpo.gov/fdsys/pkg/FR-2008-02-13/pdf/E8-2667.pdf ↩
"Cities with 100,000 or More Population in 2000 ranked by Population per Square Mile, 2000 in Alphabetic Order". United States Census Bureau, Population Division. July 10, 2008. Archived from the original on December 26, 2002. Retrieved July 13, 2008. https://web.archive.org/web/20021226215307/http://www.census.gov/statab/ccdb/cit1040a.txt ↩
"Annual Estimates of the Population for Incorporated Places in Virginia". United States Census Bureau. Archived from the original on November 5, 2007. Retrieved September 11, 2008. https://web.archive.org/web/20071105221856/http://www.census.gov/popest/cities/tables/SUB-EST2006-04-51.csv ↩
"Participant Statistical Areas Program (PSAP)". United States Census Bureau. Archived from the original on September 29, 2006. Retrieved March 9, 2008. https://web.archive.org/web/20060929001940/http://www.census.gov/geo/www/psap2010/psap2010_main.html ↩