Bureau of Justice Statistics -- The BJS provides a wealth of crime and criminal justice data compiled by the U.S. government via a variety of data-collection programs. The BJS also provides various tools to produce and download tables on topics such as crime rates, crime victimization, and corrections populations. Many of the BJS' data collections are available via the National Archive of Criminal Justice Data.
Federal Bureau of Investigation -- The FBI maintains a number of reports on crime and arrests collected via the Uniform Crime Reports data collection program. UCR data are available here in .pdf and .xls formats. The NACJD has an extensive guide for understanding, accessing, and using the various data collected via the Uniform Crime Reports.
Historical Violence Database -- The Historical Violence Database, which is hosted at the Center for Criminal Justice Research at Ohio State University, is (to quote the website) "a collaborative research project on the history of violent crime, violent death, and collective violence." Data from the project are available for the United States and other countries.
International Crime Victims Surveys (ICVS) -- A "victimization" survey performed in different countries in sweeps from 1989 onwards in which respondents are asked about their experiences with crime and with policing and about their feelings of personal safety. Different waves of the ICVS are available in various locations: the United Nations Interregional Crime and Justice Research Institute, Data Archiving and Networked Services in the Netherlands, the University of Lausanne, the National Archive of Criminal Justice Data, and openICPSR.
National Archive of Criminal Justice Data (NACJD) -- The NACJD provides online access to and analysis of crime and justice data from federal and state agencies. The data cover topics such as attitudes towards crime, crime stats from official agencies, and the functioning of the criminal justice system.
Office of Juvenile Justice and Delinquency Prevention -- The OJJDP offers both its database of National Juvenile Justice Data Sets and Data Analysis Tools as means of access to its various data collections, with a particular focus on juvenile activity in the justice system. The Statistical Briefing Book provides an overview of data collected by or related to the OJJDP. Many datasets funded by the OJJDP are also available via the NACJD.
The Songer Project -- The Songer Project at the University of South Carolina is "a comprehensive access point to the most recent and cutting-edge research on law and judicial politics. At this website, individuals interested in law and judicial politics can download electronic datasets of court cases, obtain smaller datasets or measures of judicially relevant phenomena, read various working papers on important topics, and link to other websites containing law and judicial politics information." The available datasets cover topics such as attributes of court cases and justices at various levels of government (e.g. district courts, appeals courts, the Supreme Court), measures of judicial ideology, and the institutional histories of district courts. Many of the datasets are also available via the Judicial Research Initiative. The Spaeth Supreme Court data also reside at http://supremecourtdatabase.org/.
Sourcebook of Criminal Justice Statistics -- The Sourcebook compiles data from more than 100 US criminal justice sources. Available in spreadsheet or .pdf formats.
Uniform Crime Reporting (UCR) Program Data: Arrests by Age, Sex, and Race, 1980-2016 -- Annual data for individual police agencies for counts of arrests for individual categories of crime broken down by age, race, and sex. The data were compiled by Jacob Kaplan at the University of Pennsylvania.
Uniform Crime Reporting Program Data: Offenses Known and Clearances by Arrest, 1960-2016 -- Monthly and yearly data for individual police agencies on reported offenses and cleared offenses. The data were compiled by Jacob Kaplan at the University of Pennsylvania.