Police say the child's mother was pushed during the argument, causing the car seat to fall from the railing. The baby was not strapped in and hit the ground. He was pronounced dead at Comer Children's Hospital at 12:45 a.m. Monday.
Police are investigating and have not made any arrests.
Some of the adults suffered minor stab wounds after they were cut while involved the fight.
It was not immediately known whether the death was accidental or intentional and police said as of 2:45 a.m. they were trying to interview all parties though the mother's husband allegedly fled the scene.
Chicago Police Officer Michael Fitzpatrick says the baby's mother and father were arguing on an apartment porch in the East Chatham neighborhood, when the man kicked the woman in the back as she walked down stairs. That's when the child fell from the railing.
The STNG Wire and Associated Press contributed to this report.