NHGIS Site
The National Historical Geographic Information System (NHGIS) website recently is an incredibly valuable tool for historic demographics information. You just need to register.
From their site:
The National Historical Geographic Information System (NHGIS) provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2000. NHGIS offers the following options to obtain data:
- The NHGIS Shape Finder provides access to boundary files for mapping data in a GIS software package.
- The NHGIS Data Finder provides access to aggregate census data.
- Social Explorer allows online mapping of NHGIS data