Cache County sheriff's Lt. Mike Peterson says the boy was shot in the stomach with a .22-caliber rifle Friday evening in the family's home in College Ward.
"The gun had been used earlier in the day by the victim's father and was set down after returning home," said Cache County Sheriff's Lt. Mike Peterson, according to CBS affiliate KUTV in Salt Lake City. "The gun was in an unloaded state but did have live rounds in the magazine. We believe the three-year-old had to manipulate the action enough to chamber a live round prior to the incident occurring."
All family members were home and the boy's mother immediately called for assistance.
First-responders - some just a few houses away - rushed to the home and transported the boy in critical condition to Logan Regional Hospital, where he underwent surgery, KUTV reports. An air ambulance then flew him from Logan to Primary Children's Hospital, where he died.
Peterson says while investigators believe the shooting was accidental, they'll submit a report to the county Attorney's Office for review. The office will determine whether any charges are filed.
The victim's name wasn't immediately released.
Peterson said the incident is an unfortunate reminder of an important message for families.
"It really does just reiterate that weapons are dangerous and you just need to take extra precautions with them," Peterson said. "You just can't be safe enough."