Measuring America : the decennial censuses from 1790 to 2000
Reproduces decennial census schedules and forms, 1790 through 2000. Provides history of decennial census and specific questions.

Historical Census Browser
Population and housing data for all U.S. states and counties, 1790 to 1960, based on decennial census of population and housing. Provides basic counts of population and housing, including race, gender, and some measure of household size and composition. For 1840 to 1960, economic characteristics such as education and occupation are included. Later decades have many variables, including ancestry, literacy, and income variables.

Decennials - Census of Population and Housing
PDF-format versions of historic US decennial census volumes, 1790 to present. Topics covered include basic counts of population and housing, with race and gender, for the nation, states, counties, townships and municipalities, and some small areas (e.g., wards). From 1840 to present, social and economic information is provided.
Holdings: 1790 to present (backfile in progress: 1790-1860, 1990-2000 available)

IPUMS
REQUIRES FREE REGISTRATION. Census microdata from historic national censuses, U.S. and worldwide. Only provides microdata data sets, with data subsetting and extraction, and documentation. Frequency distributions and crosstabulations not provided.