The main tool for U.S. demographics is the data compiled by the U.S. census Bureau. For more information, see Census Bureau Information entry or the links on The Demography and Housing page from the University of Michigan.
You can enter an address in the U.S. and get population (including race), income and housing data for the surrounding Metropolitan Statistical Area (MSA) using the FFIEC's free Geocoding System.
You can get demographic profiles of neighborhoods -- organized by Zip Code -- from the National Encyclopedia of Zip Code Demographics on Lexis (GEODEM;ZIPREZ). For a general idea of what kind of person lives in a particular zip code, try the free search on MyBestSegments.
Lexis also has demographics databases broken down by County (GEODEM;CNTREZ), Metropolitan Statistical Area (GEODEM;MSAREZ), Metropolitan Statistical Area/Workplace (GEODEM;MSAWRK), State (GEODEM;STAREZ), and the entire US (GEODEM;USAREZ), all provided by Nielson Claritas.
RESEARCH TIP: The Official Statement for school bond issues generally provides detailed demographic information relating to the community.
For demographic information about countries other than the U.S., see the links listed under International Demographic & Population Data from the University of Tulane. Also see the Country Information entry.