The Contra Costa County Sheriff's Office received a call at about 2 a.m. from someone at a home in the 2900 block of Mary Ann Lane in unincorporated Bay Point reporting a medical emergency, sheriff's spokesman Jimmy Lee said.
When deputies and medical personnel arrived, they found a 49-year-old man on the floor suffering from an injury.
The man was given first aid and then transported to John Muir Medical Center in Concord, where he was pronounced dead, Lee said.
The Contra Costa County coroner's office has since identified the victim as Bay Point resident Aaron Compton Jr. A deputy coroner said Compton died from a stab wound to the left side of his chest.
Lee said other people were in the home when Compton was killed, but as of about 2 p.m., the sheriff's office was not releasing any information about possible suspects and the case remained under investigation.