United States Census Bureau Data Repository (via ICPSR)
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.
These are public-use samples randomly selected from all of data collected by a census. ICPSR has microdata from the censuses of 2000, 1990, 1980, 1970, 1960, 1950, 1940, and some earlier censuses, with sampling fractions ranging from 10 to 0.01 percent.