Bureau of the Census -- official site to the Bureau with numerous links to contemporary, recent and projected census and demographic data.
Census Atlas of the United States -- provides the complete content, in PDF format, of the Atlas, a large-format publication about 300 pages long and containing almost 800 maps. Data from decennial censuses prior to 2000 support nearly 150 maps and figures, providing context and an historical perspective for many of the topics presented.
Census of Population and Housing -- data presented here ranges from our most recent census to the historical decennial census conducted throughout the decades. Some of the data were scanned as an effort to make historical census information available to the public.
National Historical Geographic Information System -- provides, free of charge, aggregate census data and GIS compatible boundary files for the United States between 1790 and 2000. NHGIS includes state and county statistical data from 1790-2000; census tract statistical data from 1910-2000; historic state and county boundary files (1790-2000) and census tract boundary files (1910-2000); all summary data (at all summary levels, including census blocks) from 1970-2000; and, County Business Patterns data from 1970-2000.