The Bureau of Justice Statistics provides statistical reports on crime, criminal justice, law enforcement, and criminals in the United States. Some data sets are available for downloading.
This site contains data from the Federal Bureau of Investigation's Uniform Crime Reporting system on reported crimes and arrests for U.S. counties dating from 1990 until the present.
Crime statistics from 1995 to present are reported for the nation as well as for individual regions, states, counties, cities, towns, and college campuses. Data is available in PDF.