(Gift link)
The Gun Violence Archive, a nonprofit research group that tracks gun violence using police reports, news coverage and other public sources, defines a mass shooting as one in which at least four people were killed or injured. It counted more than 300 such shootings through early July. Of those shootings, 15 involved four or more fatalities, including one at a July 4 celebration in Highland Park, Ill., in which at least six people were killed.
Last year:
The group recorded 692 mass shootings last year, with 28 involving four or more fatalities.

ETA: One more today. Let freedom ring.
I do not care for “mass shooting” numbers. Most numbers in criminal and other reports can be changed fairly easily. A robbery becomes missing property. Four people injured can be fixed to three or five, depending on what point you want the numbers to support.
Further, are those killed or injured by other means less worthy of our consideration? Why only shootings?
The one thing that is hard to fix is the number of dead bodies. We might argue if a death is a result of an accident or a crime, a homicide or a suicide, but the number of the dead remain the same.
This is why I keep the only list of US mass killings. I suspect there are truths in my numbers that might be homogenized out of more processed numbers. Or perhaps not. I am often wrong.