Officials say those involved were adult family members of the shooter, who died by suicide on Friday.
They were found in the family's home on the outskirts of Douglas, a small city roughly 320km southeast of Atlanta.
"Investigators believe this was an apparent murder-suicide involving immediate family members who reside in the home," said Douglas Police Chief Brannen Pruette during a news conference on Saturday.
Officers responded to an emergency call made by one of the victims shortly after 11pm and found a woman alive at the scene. After transport to a nearby hospital, she was pronounced dead, raising the death toll to five.
Earlier in the day, police confirmed that woman made another emergency call and summoned officers to the house.
"It's my understanding the call was placed by the wife, the female victim. She called, and was complaining about the husband who was in the house smoking and she said he was killing her with the smoke," Pruette said.
Last weekend, two people were killed and 35 injured in a shooting during a block party celebrating a high-school football game in Vienna, another small city just an hour north of Douglas.
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