Basic Census Geography currently in use: (state, county, tract, block-group, block). Note: Data is also aggregated for "place" (cities and towns) and other political/administrative divisions such as census county divisions (ccd) and municipal civil divisions (mcd).
Please Note: Many statistics are collected only through a sample count. This means that there are fewer statistics available for the smaller geographies. In addition, some data is suppressed for very small geographic areas, e.g. census blocks, to protect individual privacy.
1790 - 2010: Social Explorer.
Includes data from the Decennial Censuses (back to 1790), the American Community Survey (2005 --) ,along with other datasets not derived from the census,such as religion data (back to 1980).
1970-2010, reallocated to 2010 census boundaries: Social Explorer: Tables
U.S. Decennial Censuses on 2010 Geographies provide reallocated data from Decennial Censuses on 2010 geographies. "Reallocation of decennial census data on 2010 geographies was performed using reallocation fractions from Longitudinal Tract Data Base (LTDB). Data is available on census tract, county, state and nation level geographies. The form of this survey, as well as the datasets and tables it contains, is kept similar to our corresponding Decennial Census surveys. See: Reallocating Census Data: How Social Explorer Makes Cross-Decade Comparisons Possible."
Note: Social Explorer does not include the non-decennial (intercensal) data from 1790 to 1945, generally known as the "Dubester set" (referencing a guide issued by the Library of Congress).
Prior to 1980, you may find that some areas are represented only by numeric codes. To identify the correct code for the area you need, see: https://www.census.gov/programs-surveys/metro-micro.html
1790 - National Historical Geographic Information System
The National Historical Geographic Information System (NHGIS) provides free online access to summary statistics and GIS boundary files for U.S. censuses and other nationwide surveys from 1790 through the present. Includes some geographies not represented in Social Explorer, above.
1960 - 2010: Geolytics CDROM
Note: The NCDB (National Change Database) disk includes 1970 - 2010 data, normalized to 2010 boundaries, down to the tract level. Unfortunately, Geolytics, a proprietary company, does not share it's methodology. Compare with Social Explorer Reallocated tables, above. See also: Validating Population Estimates for Harmonized Census Tract Data, 2000–2010 comparing NCDB with LTDB and NHGIS
Beginning in 1940, the census began to incoporate sampling procedures to collect supplementary data (released as supplementary reports of various kinds).
In 1960, the census was conducted using a short form, asked of every household, and a much longer, two-part form, asked of 20% of households.
By 1970, a short form went out to every household, and the long form, sample data, was asked of 1-in-6 households.
1980 - 2000:
SF 1 -- Data is from the short list of questions asked of every household
SF 3 -- Data is from a much longer, more detailed, list of questions asked of 1-in-6 households
In 2010 -- A brief questionnaire is sent to every household. More detailed data is available from the American Community Survey (ACS). The ACS is a continuous, "rolling" survey of 1-in-8 households. Data is released in 1-year, 3-year, and 5-year estimates.
SF 1-- Data is from a short list of questions asked of every household
ACS (American Community Data) Sample Data: CQ Press Guide to the American Community Survey of the US Census Bureau
Some geographies other than county, state, and tract, which can be found in print reports for the older decennial censuses or in the National Historical GIS (www.nhgis.org), are not available in Social Explorer.
An example is the Standard Metropolitan Statistical Areas for 1960 (or places for 1980).
In addition, Social Explorer does not include the non- decennial (intercensal) data from 1790 to 1945, generally known as the Dubester set (referencing a guide issued by the Library of Congress).