Can I get the original data?
For all census years from 1850 to 1950 (except for 1890, which was destroyed by fire), the original manuscript population schedules are preserved on microfilm at the National Archives in Washington D.C. In each year, the microfilm reels and the schedules within reels are organized geographically: alphabetically by state, within states alphabetically by county, and within counties numerically by enumeration district. For census and ACS years since 1960, the census schedules exist in fully machine-readable form.
The basic sources for most of the IPUMS documentation are the documentation provided for each of the individual public use microdata samples. All of them should be available through the Inter-university Consortium for Political and Social Research (ICPSR), P.O. Box 1248, Ann Arbor, MI, 48106.