IPUMS — USA

http://www.ipums.org/usa/

The IPUMS database is a nationally representative high-precision series of census microdata files spanning the period from 1850 through 2000.  It represents a twelve-year effort to create an integrated census database describing the American population from the mid-nineteenth century to the present.  The IPUMS includes historical samples created at Minnesota for every surviving census from 1850 through 1920.  For the period from 1940 through 2000, the IPUMS incorporates samples that were originally prepared by the Census Bureau.