The Census Bureau serves as the leading source of quality data about the nation's people and economy.
Maps and Data: http://www.census.gov/geo/maps-data/index.htm
Find geographic data and products such as the TIGER/Line Shapefiles, KMLs, TIGERweb, cartographic boundary files, geographic relationship files, and reference and thematic maps.
Census Data Mapper http://www.census.gov/geo/maps-data/maps/datamapper.html
The Census Data Mapper is a web mapping application intended to provide users with a simple interface to view, save and print county-based demographic maps of the United States. The data are from the 2010 Census.
Resource URL: http://www.census.gov/