-- The shooting in California Wednesday that left 14 dead and another 21 wounded was at least the 57th mass shooting in 2015 where three or more people were killed, according to the ABC News analysis.
The analysis used Reddit's Mass Shooting Tracker, which defines a "mass shooting" as any event where four or more people are shot.
The federal definition of a "mass killing” is “three or more” people killed, according to an FBI study on active shooters.
ABC News examined the attacks in which the Tracker identified three or more people killed -- which include the shooter in some cases.
There was at least one shooting every month and in three cases, two in a single day.
With six incidents, Texas had the most mass killings, including a biker shootout in Waco that left nine dead and campsite attack in Anderson County that left six dead.
A month later, a gunman opened fire on two military installations killing four Marines and a Navy Petty Officer. A massacre at an Oregon community college left 10 people dead when a gunman opened fire in a classroom.
While these shootings gained national attention, there were many others that did not have the same notoriety.
Many of the shooting deaths involved domestic incidents, some were suspected gang activity and others were people caught in the crossfire. These shootings took place across the country and impacted people of all races, cultures and socio-economic classes.
All of the incidents involved firearms, but some of the victims died by other means. Federal data on mass killings was not available for 2015.
Following Wednesday's attack, President Obama called on the federal government to take steps that would "make it make it harder, not impossible, but harder to individuals to get access to weapon."
"I do think that as the investigation moves forward it’s going to be important for all of us, including our legislatures, to see what we can do to ensure that when individuals decide that they want to do somebody harm, we’ll make it a little harder for them to do it," he said.
"What we are trying to do is make sure our response actually addresses the problems without infringing upon the rights of law-abiding citizens, Ryan said Thursday to CBS "This Morning". "A lot of these people who are getting guns who are mentally unstable, who should not be getting guns and this is a gap in our laws that we feel needs to be filled.