From a U.S. Census E-Mail:
[Data] files contain demographic, economic and governmental statistics from the Census Bureau and other federal agencies, presented for the purpose of multi-county comparisons or single county profiles. National- and state-level statistics are presented as well. The files cover topics such as agriculture, crime, education, health, retail trade and vital statistics. New in this update are additional statistics from the 2005-2009 American Community Survey for economic and housing characteristics and 2010 federal spending.
Direct to USA Counties Web Site