New London: Historical Research Guide: Data

Obtaining recent (2010-) Census data for New London is pretty straightforward using the tools listed below. Finding historic Census data for New London is a more involved process.

One can pretty easily use the Census of Population and Housing PDFs listed below to obtain data at the town or place level, but it is more difficult to find good historic data for New London below the town level, such as at the level of Census Tracts or Block Groups. 

Census Tracts were invented in 1910 and were only applied to a very few metropolitan areas.  Their use has grown over time, and only with the 2000 census was every square inch of the United States put into census tracts.  Prior to census tracts, very limited information was provided by city "Wards" (Source for this information).

While individual Census returns are available for New London from 1940 - the latest date for which individual returns have been made public - we do not seem to see the Census Tract in use for New London until the 1970 Census. 

Source: The above population data were manually collected from Census of Population and Housing.

Understanding Census geography is a complicated but critical component of finding and using Census data. The fact that Census geographies are not absolute truths (they changed over time) makes comparing historic data even trickier. For example, the boundaries of a Metropolitan Statistical Area may have expanded or contracted from one decade to the next, so any comparison between them is not necessarily based on like or comparable units of measurement.

Counties and equivalent areas are the primary divisions of most states, Puerto Rico, and the Island Areas. These are not uniform and have changed over time. For example, the Census Bureau still uses the counties for Connecticut even though they have been dissolved as legal entities.

Minor Civil Divisions (MCDs)/Census County Divisions (CCDs) MCDs are legally defined county subdivisions, such as towns and townships. In 21 states where MCDs do not exist or are not adequate for reporting subcounty statistics, the Census Bureau, in cooperation with state and local officials, delineates county subdivisions known as Census County Divisions.

Places are concentrations of population such as cities, that have legally prescribed boundaries, powers, and functions. Other population centers without legally defined corporate limits or corporate powers are defined by the Census Bureau in cooperation with state officials and local data users. These are called Census-Designated Places (CDPs) and are identified in data tables by the acronym CDP following the place name.

Census tracts generally contain between 1,000 and 8,000 people with an optimum size of 4,000 people. Census tract boundaries are delineated with the intention of being stable over many decades, so they generally follow relatively permanent visible features. However, they may follow governmental unit boundaries and other invisible features in some instances; the boundary of a state or county is always a census tract boundary. Block Numbering Areas (BNAs) are now called census tracts. Census tracts are probably the most commonly-used geography by statisticians and policymakers. Click here to see the 2020 Census Tract map for New London.

Block groups are statistical divisions of census tracts, and generally contain between 600 and 3,000 people (optimum size is 1,500). They are a collection of census blocks within a census tract following physical boundaries and sharing the same first digit of their four-digit identifying numbers.

Blocks are statistical areas bounded by visible features, such as streets, roads, streams, and railroad tracks, and by nonvisible boundaries, such as selected property lines and city, township, school district, and county limits and short line-of-sight extensions of streets and roads.

Source: Most of the above language was copied from this University of Pittsburgh Library Guide.