1990 Demographic Profile Generator (U.S.)--The generator allows you to create a demographic profile for a particular census grouping (e.g., census tract, block group, city, etc.) by entering in FIPS codes, zip codes, etc. There is also a link for code lookup.
American FactFinder--The American FactFinder is an extensive source for census statistics from the U.S. Census Bureau. Users can create data tables from the Decennial Census (2000 and 2010), the American Community Survey (2000-present), and the Economic Census (1997, 2002, and 2007) and download those tables into spreadsheet files. See http://factfinder2.census.gov/faces/nav/jsf/pages/what_we_provide.xhtml for a list of available data collections..
CDC Wonder Population Information--CDC Wonder includes a site that provides population estimates for different age, race, and gender groups. Users can get estimates at the national, state, or county levels, from 1990 onwards.
Census Bureau (U.S.)--The Census Bureau gathers a dizzying amount of social, demographic, and economic information about the United States through various means. The Subject Index is a good starting point for browsing and searching through the Bureau's wealth of information.
Census Bureau Population Estimates--The Census' Population Estimates site provides annual population estimates for different categories of age, race, and gender, extending back to 1970. Estimates are at the national and state levels, with some additional estimates for counties and metro areas.
Current Population Survey Table Creator--The CPS Table Creator is a convenient way of generating summary tables and breakdowns for topics such as health insurance or poverty or education attainment, drawing on data from the Annual Social and Economic Supplement of the CPS.
Data.Gov--Data.Gov is a central portal for datasets, both statistical and geospatial, that are produced by the Federal Government of the United States. While the site is not exhaustive in its coverage, it does include data from multiple agencies within the federal government. The data catalog is located at http://explore.data.gov/.
Historical Census Browser--The Geostat Center at UVa has compiled county-level data from the U.S. Census from 1790 to 1960 (using data from ICPSR #0003) and made that data available via a very-user friendly web brower.
Human Mortality Database (HMD)--The HMD (which requires a free registration) contains population data (e.g. mortality, life expectancy) for many countries (largely from the OECD) and links to related external sites.
ICPSR Census 2000 site--This is a special site from the ICPSR with Census 2000 data. Data are available in various geographies and formats, including microdata files.
SimplyMap--SimplyMap is an Internet-based mapping application that enables users to develop interactive thematic maps and reports using thousands of demographic, business, and marketing data variables. Users can download data in spreadsheet-friendly formats and also use data with GIS software. Go here for a quick guide to SimplyMap. SimplyMap is also available via Databases at Emory.
Social Explorer--Social Explorer provides quick and easy access to current and historical census data and demographic information. Its contents include the entire U.S. Census from 1790 to 2010, annual updates from the American Community Survey, data on religious congregations for the United States for 2009, decennial religious congregation data for 1980-2010, and carbon emissions data for 2002. Users can create reports and maps at various levels of geography, including counties, Census tracts, Census block groups, and zip codes, depending on data availability. Social Explorer is also available via Databases at Emory.
State and County Quick Facts--This site contains a clickable map of the US to obtain demographic profiles of different states. The subnational level data is subsequently compared with the U.S. as a whole. There is also a significant amount of data from the 2000 and 2010 censuses.
Statistical Abstract of the United States--Electronic version of the popular resource. The Statistical Abstract contains a wealth of information on numerous socio-economic and demographic indicators for the US. Historical data tables taken from the Statistical Abstract are available here. There is also a CD version of the Statistical Abstract available in the Data Center.
U.S. Citizenship and Immigration Services Immigration Statistics--U.S. Citizenship and Immigration Services (formerly the INS) publishes the Yearbook of Immigration Statistics and other collections of statistical information on topics such as immigration flows, immigration enforcement, and estimates of unauthorized immigration populations.
World Population Prospects-- This database is produced by the United Nations' Population Division and contains cross-national data on basic population demographics and vital statistics (e.g. birth and death rates, maternal mortality, population by age and gender and urban/rural areas).