IPUMS
REQUIRES FREE REGISTRATION. Census microdata from historic national censuses, U.S. and worldwide. Only provides microdata data sets, with data subsetting and extraction, and documentation. Frequency distributions and crosstabulations not provided.

ICPSR
USE OF ICPSR DATA REQUIRES STATISTICAL PROCESSING SOFTWARE AND GZIP DECOMPRESSION SOFTWARE. Direct-download access to social science quantitative data sets archived by ICPSR. Subjects covered include political science, sociology, demography, history, economics, communication, international relations, gerontology, public health, criminal justice, and education. The ICPSR archive includes almost all major studies in the social sciences, including the General Social Survey and International Social Survey Program, decennial Census of Population and Housing, American National Election Study, Eurobarometer, Voter News Service exit polls, US Congressional and UN roll call votes, National Crime Victimization Survey, and public opinion polls. Special topic archives, with limited interactive tabulation and extraction capability, cover health and medical care, international education, aging, criminal justice, and substance abuse and mental health.
Holdings: 1962-present.