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 place population did not begin until the 1880 census. That census also marked the first systematic identification and reporting of unincorporated communities, which appeared in separate tables for each State.

Some unincorporated places first were reported in statistical tables in the 1850 census, usually appearing under the appropriate MCDs. After the clarification and expansion of this reporting in 1880, the 1890 decennial census intermingled incorporated and unincorporated places without distinguishing them. The next four decennial censuses did not include unincorporated communities.

For the 1940 decennial census, the Census Bureau compiled a separate report of unofficial, unincorporated communities of 500 or more people. The Census Bureau identified many of the communities in advance with mapping assistance from the U.S. Public Roads Administration, but also relied on census enumerators to identify and approximate the boundaries of additional communities. Many of the unincorporated communities included in the special 1940 report were not communities in the sense of being cohesive, locally recognized settlements; rather, they often were merely residential subdivisions or clusters of housing units.

The Census Bureau officially recognized unincorporated places in the decennial census of 1950, identifying all potential areas in advance of the count, including them on census maps, and adding them to its geographic coding framework. It established a population minimum of 1,000 and used the symbol (U) to identify them in the decennial census reports of 1950, 1960, and 1970. This designation changed to CDP in the 1980 census.

Many of the residential subdivisions included in the 1940 Unincorporated Communities report were included in the new urban fringe delineations in the 1950 census without separate identification. Unincorporated places were not identified within UAs until the 1960 census, when the Census Bureau established a 10,000 person population minimum. The Census Bureau has modified the population threshold for identifying unincorporated places within UAs with each subsequent decennial census to the 9-22Places