American Fact Finder - Uses U.S. Census Bureau data--population, housing, economic, and geographic--to create tables, reports, and maps down to the census block level. Data sets are listed by program area (census or survey) and year. Site includes community profiles; data on age, education, income, and race; home values, ownership, and mortgage information; and information on foreign trade, governments, and housing starts.

Census of Agriculture - "The only source of uniform, comprehensive data on agricultural production and operator characteristics for each county, state, and the Nation." Includes maps on many agricultural themes, statistics by congressional district, and a database of crops and livestock. The census is conducted in years ending in 2 and 7; the site provides the current and the two previous reports. Searchable. From the USDA's National Agricultural Statistics Service (NASS).

Historical Census Browser -"The data presented here describe the population and economy of U.S. states and counties from 1790 to 1960."  Start with one of the decennial census pages, and then select the variables you want to view. Data is initially displayed by state. County data can be displayed by selecting any or all states from the state display. From the Geospatial and Statistical Data Center, University of Virginia.
 

State and County Facts - Selected quick facts and statistics on individual state population and business. Includes land area and population figures.
 

Statistical Resources on the WEB - Annotated directory of websites providing statistics on agriculture, business, housing, labor, science, transportation, and other topics.

U.S. Census Bureau Maps and Cartographic Resources -