Q. Where can I find reliable data on mass shootings in the United States?

There is no one definition of "mass" shooting, and there is no one source that has complete data, so be careful in your research.

Take a look at these sources for background information:

What is a Mass Shooting? WAMU's Guns and America

HeinOnline's Gun Regulation and Legislation in America (subscription available to the AU community: Research Assistancee > Databases > HeinOnline)

Firearms and Violence: A Critical Review National Academies of Sciences. Uses conventional standards of science to examine three major themes - firearms and violence, the quality of research, and the quality of data available. The book assesses the strengths and limitations of current databases, examining current research studies on firearm use and the efforts to reduce unjustified firearm use and suggests ways in which they can be improved.

What's More Common: A 'Good Guy' Without a Gun or a 'Good Guy' with one?  The Washington Post "The Fact Checker" Feb. 5, 2023.

Datasets & Statistics:

ALERRT Active Attack Data  project of the Advanced Law Enforcement Rapid Response Training Research Team (Texas State University) that provides up-to-date active attack data regarding events, shooters, weaponry, and resolution of active shooter events. ALERRT also analyzes vehicle attacks, knife attacks, and any other type of event where mass murder is the primary intent. 

Firearms Mortalities by State - Centers for Disease Control (CDC)

Gun Violence Archive (GVA) is a nonprofit research group with accompanying website and social media delivery platforms which catalogs gun violence in the United States. It was founded in 2013 by Michael Klein and Mark Bryant. Klein is the founder of Sunlight Foundation, and Bryant is a retired systems analyst.

ICPSR: Inter-University Consortium for Political and Social Science Research This link opens in a new window . Search for mass shootings in this resource which includes both publicly available and non-publicly available datasets on public policy and social science research. NOTE: Access to datasets requires a free user-specific login. To log in using your existing account or to create a new account, click on "MyData Login/Create Account" from the ICPSR page. To download data from ICPSR, please refer to this Subject Guide.

K-12 School Shooting Database : Compiled by the Naval Postgraduate School’s Center for Homeland Defense and Security (CHDS), the K-12 School Shooting Database research project is a widely inclusive database that documents instances when a gun is brandished, is fired, or a bullet hits school property for any reason, regardless of the number of victims, time, day of the week.

Mother Jones US Mass Shootings, 1982-present: Data From Mother Jones’ Investigation database originally covered cases from 1982-2012 and has since been updated and expanded numerous times. For analysis and context on this data—including how they built the database, and a change to the baseline for victim fatalities with cases dating from January 2013—see our Guide to Mass Shootings in America, which includes an interactive map documenting all of the cases.

National Violent Death Reporting Service The CDC's NVDRS is an incident-based system, which can link deaths of the same violent event to help identify the circumstances of multiple homicides (such as mass shootings) or homicides followed by suicides.

Stanford University Library's Mass Shootings in America (MSA)  The Stanford MSA is a data aggregation effort. It is a curated set of spatial and temporal data about mass shootings in America, taken from online media sources. It is an attempt to facilitate research on gun violence in the US by making raw data more accessible. It is no longer maintained; however, the data is available through Github.

The Violence Project’s Mass Shooter Database contains extensive details about public mass shootings in the US and their perpetrators, weapons, and victims, with a goal of “finding pathways to prevention.” The database, funded by a National Institute of Justice grant, covers 170+ shootings between 1966 and early 2020. Examples of the variables include: the perpetrator’s employment status, known prejudices, and experience with mental illness; the victims’ relationship to the perpetrator and estimated years of life they lost; and the firearms’ make, model, and method of acquisition.

Washington Post Analysis. (unfortunately no longer being updated) The Post's relational database allows user to search for details of a shooting or refine searches based on number of fatalities or injuries.

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