(CNN)Two people were killed and at least another dozen were injured as shots rang out at a house party in Illinois where people were gathering for Halloween.
It was one of at least 11 mass shootings in the US over the holiday weekend, including several at places where crowds had assembled.
The violence left at least 12 people dead and another 52 injured, according to CNN reporting and an analysis of data from Gun Violence Archive and local news and police reports. CNN defines a mass shooting as an incident with four or more people killed or wounded by gunfire, excluding the shooter.
The number of mass shootings in the US increased during the coronavirus pandemic. There have been 599 mass shootings so far this year, according to the archive. There were 611 in 2020 and 417 in 2019, the group said.
The increase in mass shootings during the pandemic is consistent with the notion that the violence may be influenced by social and economic factors, researchers have said.
Over the weekend, gunfire erupted at house parties, a boxing event and on the streets. These are the mass shootings that took place across seven states.
Illinois: 3 weekend mass shootings
Two people were killed and at least 12 others were injured in shooting early Sunday at a Halloween party in Joliet Township, Illinois, according to the Will County Sheriff's Office. Joliet is about 40 miles southwest of Chicago.
A sheriff's patrol sergeant responded after hearing 10 to 12 gunshots, the sheriff's office said in a news release. The sergeant saw more than 100 people fleeing eastwards along the street.
The shooting occurred near a DJ booth set up in the backyard of a residence, law enforcement personnel determined, the news release said. Witnesses told detectives two people fired on the crowd of nearly 200 from a porch overlooking the party, according to the news release.
The identities of the deceased will not be released until their families are notified, the sheriff's office said.
In Decatur, Illinois, about 40 miles east of Springfield, another shooting incident at a large gathering left one person in critical condition and three others with non-life-threatening injuries, according to police.
Officers responded around 3:30 a.m. Saturday to reports of multiple shots fired and found a 29-year-old man with multiple gunshot wounds, the Decatur Police Department said in a statement. Three other shooting victims later presented at hospitals, and it was learned they sustained their injuries in the same incident, police said.
"Officers determined that a large house party in the 1100 block of N. Union, attended by upwards of 100 people had been taking place when multiple shots were fired by multiple shooters," according to the release.
Very few witnesses had come forward, said police, who appealed for more information.
Meanwhile, police in Flossmoor, Illinois, south of Chicago, found four people with gunshot wounds early Sunday after responding to calls of a disturbance and gunfire, CNN affiliate WLS reported, citing officials.
Paramedics worked at the scene before all four victims were taken to hospitals, WLS said.
Police said they believed it was an isolated incident, WLS reported.
Colorado: 2 killed, 2 injured
Two people were fatally shot Sunday morning in a commercial area of Lakewood, Colorado, CNN affiliate KCNC reported.
One person died at the scene, and another succumbed to injuries at a hospital, according to police, per KCNC.
Two other people who were shot were taken to the hospital on their own, KCNC reported.
Kentucky: 2 killed, 2 injured
Two people died after being shot early Sunday morning in Louisville, Kentucky, according to a news release from police provided to CNN by affiliate WAVE.
Louisville Metro Police Department officers responded to reports of a shooting near a gas station, where preliminary investigation suggested an altercation had taken place, the agency said. Emergency services took two men believed to be in their twenties to a hospital with gunshot wounds and both died, police said.
"As the investigation continued, detectives were informed by University Hospital that two other individuals, who appear to be in their 20s and who also may be connected to this incident had shown up by private vehicle, with gunshot wounds," police said. The severity of their injuries was not immediately known.
Texas: 2 dead, 12 wounded in separate shootings
An 18-year-old woman was fatally shot and three others, including a 16-year-old boy, were wounded after a shooting early Sunday at a party in Houston, police said.
The Houston Police Department got "a shooting in progress" call shortly after midnight, Assistant Chief Yasar Bashir said at a news conference.
"Upon arrival, they found that this location was having a house party with a very large crowd and the crowd was dispersing when the officers arrived," he said. Officers began searching around the house for potential victims and, after finding the 18-year-old woman deceased, extended their search into the streets around the house.
Officers found evidence of a shooting at the rear of the house as well as on the street, Bashir said. "They found one weapon in the ditch, and we're going to try to find out if that gun was used in the commission of this crime or not," he said.
The 16-year-old and two "young adults" were later found to have been taken to hospitals by private vehicles.
Police had one possible suspect and anticipated that there would be more witnesses "and possibly more victims because everybody left the location," said Bashir, who encouraged anyone with information to call police.