National Historical Geographic Information System (NHGIS)

http://www.nhgis.org/

The National Historical Geographic Information System is creating a database incorporating all available aggregate census information for the U.S. between 1790 and 2000.  This project includes all surviving machine-readable aggregate census data for the U.S. and will add new data transcribed from printed and manuscript sources.  The data will be freely disseminated on the web in a Geographic Information Systems framework.  We are creating new census tract maps back to 1910, state and county maps to 1790, and additional maps where feasible.  Availability of high-quality boundaries for key statistical areas will allow us to reconcile changes in census geography.  Census data, XML encoded metadata, and boundary files will be disseminated through an integrated web-based data access and mapping system.