Online Census Data
U.S. Population Statistics
Most of the printed volumes that were produced by the U.S. Census Bureau from 1790 to 1990 are available in the Government Publications section on the lower level. 1790-1940 are shelved by Dubester Number in the Dubester section. 1950 to the present are arranged by Superintendent of Documents number in the Federal Government Documents section.
U.S. Census Bureau (http://www.census.gov) - Most of the demographic data from the 1990 Census of Population and Housing along with many Census Bureau publications that have appeared since 1990. The search engine that will access available 1990, 2000 and 2010 census data and data from the American Community Survey is called the American Factfinder (factfinder.census.gov/servlet/BasicFactsServlet).
Historical Census volumes in pdf format - original volumes in electronic format. 1790 through Census 2000.
Statistical Abstracts of the United States - 1878 through 2010 in pdf format. Historical Statistics of the United States 1789-1945 is also avaiable here in pdf and Excel format.
Historical Census Data Browser - selected data from the 1790 through 1960 U.S. Censuses. User can create data maps and customized tables.
Susan B. Carter. Historical Statistics of the United States : Earliest Times to the Present. New York. Cambridge University Press. 2006. REF HA 202 H57 2006.
SimplyMaps – Demographic and Economic data from 2000 to the present.
Indexes to U.S. Census publications
Suzanne Schultz : Population Information in 19th Century Census Volumes. University of Northern Colorado. 1982.
Suzanne Schultz : Population Information in 20th Century Census Volumes. 1900 - 1940 Censuses. Oryx Press. 1985.
Kevin L. Cook : Dubester's U.S. Census Bibliography with SuDocs Class Numbers and Indexes. Libraries Unlimited. 1996. This is a reprint and update of Henry Dubester's Catalog of United States Census Publications, which is accessible on books.google.com.
The Monthly Catalog of U.S. Government Publications, located in the Government Publications Sections, provides some access to Census volumes from 1920 to 1990. It's not the best but it's all that exists for 1950 to 1970.
The Source (the Libraries' online catalog) and the provides some access to Census data from 1970 Census to the present. Make sure and limit your search to "Government Publications". Also try the Catalog of U.S. Government Publications for accessing Census Publications from 1976 to the present.