The SUV drove away from the South Side neighbourhood, leaving two people, both male, in critical condition following the shooting late on Friday, police said in a news release.
One suffered a gunshot wound to the thigh.
The eight men and four women in the group ranged in age from 17 to 47.
They were being treated at four hospitals.
Police said another man suffered unknown injuries and refused medical treatment.
Police initially responded to a call of one person shot, and found a woman with two gunshot wounds to her back and a man with four graze wounds to his back.
Both were listed in fair condition.
Detectives were investigating.
Police reported at least 21 people shot in the city since Friday evening, resulting in four deaths.
The shootings happened on Juneteenth, a holiday that celebrates the end of slavery in the United States.
Earlier Friday, former president Barack Obama and former first lady Michelle Obama welcomed the first visitors to his presidential centre on the South Side.
Pastor Donovan Price, a local advocate for gun crime victims, told CBS News that seeing a mass shooting like this on the holiday is a tragedy.
"It should be celebrating," he said.
"Fireworks should not turn into gunshots."
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