Historical Census Data Sources
From the Census Bureau's Question and Answer Center come the question-"
Where can I find historical census data on the population?"
And the answer is:
"In addition to our Selected Historical Decennial Census Population and Housing Counts, 1790 to 1990, for all geographic areas in the United States, there are three major sources of historical decennial census data:

Historical Census Reports - Contains scanned copies of all decennial census printed reports from 1790 to 2000 in PDF or ZIP format. Any data missing from these files may be requested by contacting the Main Census Bureau Library on 301-763-2511.

Measuring America: The Decennial Censuses from 1790 to 2000 - This report includes the census questionnaire and instructions for each census and individual census histories are also provided.

Historical Statistics of the United States, Colonial Times to 1970 - This section provides data from the Statistical Abstracts from 1900 to 2010, the Bicentennial Edition, Part 1 and Part 2 , and Historical Statistics for the U.S.from 1789 to 1945.

In addition to the above, the Federal Depository Library Program (FDLP) (http://www.fdlp.gov/) provides local access for census data users. Libraries designated as FDLPs maintain census publications and products as part of their existing collection and are responsible for assuring that the public has free access to these materials. Each Congressional District has at least one FDLP. Libraries identified as Regional Depository Libraries (one per state) have extensive collections of census publications and electronic products. Other FDLPs often have a more limited selection."