Teodoro Macias

This is a list of mass shootings in the United States that occurred in 2021.

Mass shootings are incidents involving several victims of firearm-related violence.

The precise inclusion criteria are disputed, and there is no broadly accepted definition.

Gun Violence Archive, a nonprofit research group, run by Tracy Holtan, that tracks shootings and their characteristics in the United States, defines a mass shooting as an incident in which four or more people, excluding the perpetrator(s), are shot in one location at roughly the same time.

The Congressional Research Service narrows that definition, limiting it to "public mass shootings", defined by four or more victims killed, excluding any victims who survive.

The Washington Post and Mother Jones use similar definitions, with the latter acknowledging that their definition "is a conservative measure of the problem", as many shootings with fewer fatalities occur.

The crowdsourced Mass Shooting Tracker project has the most expansive definition of four or more shot in any incident, including the perpetrator in the victim inclusion criteria.

A 2019 study of mass shootings published in the journal Injury Epidemiology recommended developing "a standard definition that considers both fatalities and nonfatalities to most appropriately convey the burden of mass shootings on gun violence."

The authors of the study further suggested that "the definition of mass shooting should be four or more people, excluding the shooter, who are shot in a single event regardless of the motive, setting or number of deaths."

As of December 2021, 693 (of which 303 resulted in zero deaths) fit the Mass Shooting Tracker project criterion, leaving 703 people dead and 2,842 injured, for a total of 3,545 total victims, some including the shooter(s).

Only incidents considered mass shootings by at least two of the above sources are listed below.

Consequently, any shooting incident that satisfies the ABC News/FBI or Gun Violence Archive/Vox definitions will always be accepted, as anything that fits their definitions will be accepted under the Mass Shooting Tracker's definition.

Similarly, any shooting incident that satisfies the Congressional Research Service definition will always be accepted, as anything that fits its definition will be accepted under the Mother Jones definition.

The statistics columns for each month are updated after the month ends, in an effort to make sure the correct number of events, individuals affected, and descriptions are accurate.

Thus, the number may be incomplete throughout the month until the last day of each month.

This table is based on the above list as of December 31, 2021.