Bureau of Justice Statistics

• Their Data page
• Their 'Just the Stats' search results page
• Their Publications page

Department of Homeland Security

• Immigration Data

Department of Justice

• Statistics

FBI

• Crime Data Explorer
  • The digital front door of the FBI’s Uniform Crime Reporting (UCR) Program

ICPSR Institute for Social Research, University of Michigan

• National Archive of Criminal Justice Data

Mass.gov

• Court Data, Metrics & Reports
• MA Dept. of Correction Research Statistics and Reports

• How to request research access to MA criminal record data

National Institute of Justice

• Datasets from NIJ-Funded Research

Office of Juvenile Justice and Delinquency Prevention (OJJDP) :

• Statistical Briefing Book

Pew Research Center

• Criminal Justice Publications
• Dataset and survey question access

TracReports 

• "Your source for comprehensive, independent and nonpartisan information about federal enforcement, staffing and spending."

United States Sentencing Commission

• Research (statistics and data)