The Integrated Public Use Microdata Series (IPUMS-USA) consists of more than sixty integrated, high-precision samples of the American population drawn from sixteen federal censuses, from the American Community Surveys of 2000-present, and from the Puerto Rican Community Surveys of 2005-present. IPUMS is not a collection of compiled statistics; it is composed of microdata which requires statistical analysis software (SAS, SPSS, Stata, R, etc.) to view and manipulate.

Alongside the Census Bureau datasets which have been available through ICPSR for decades this repository also makes available survey instruments, specifications, data dictionaries, codebooks, and other materials provided by the Census Bureau.

ICPSR archives and disseminates census data acquired from the United States Census Bureau as well as files prepared by ICPSR and other principal investigators. Both microdata and aggregate data constitute ICPSR's census holdings. The microdata comprise individual responses to census questions while the aggregate data contain tabulations of the individual responses at various aggregate levels of observation such as states, counties, places, and census tracts.

2000-present. ACS PUMS Documentation

1% and 5% Public Use Microdata Samples (PUMS) are linked here for Census 2000 and 1990. 1980 files are described and also available from the National Archives