"The FBI's UCR [Uniform Crime Reporting] Program is a nationwide, cooperative statistical effort of more than 18,000 city, university and college, county, state, tribal, and federal law enforcement agencies voluntarily reporting data on crimes brought to their attention. Since 1930, the FBI has administered the UCR Program and continued to assess and monitor the nature and type of crime in the Nation. The program's primary objective is to generate reliable information for use in law enforcement administration, operation, and management; over the years, however, the data have become one of the country's leading social indicators. Criminologists, sociologists, legislators, municipal planners, the media, and other students of criminal justice use the data for varied research and planning purposes. In 2011, law enforcement agencies active in the UCR Program represented more than 304 million United States inhabitants (97.8 percent of the total population). The coverage amounted to 98.8 percent of the population in Metropolitan Statistical Areas, 92.3 percent of the population in cities outside metropolitan areas, and 93.1 percent of the population in nonmetropolitan counties."
Federal Bureau of Investigation: http://www.fbi.gov/