There's no word on the circumstances surrounding the shooting.
Martinez was pronounced dead at Mount Sinai Hospital at 9:09 p.m. Monday, the Cook County Medical Examiner's office said.
Police were called to the Avers address at 8:48 p.m. for reports of a person shot and found a victim outside on the ground with a gunshot wound to his head, according to police News Affairs Officer Daniel O'Brien.
The shooting is believed to be gang related and no one is in custody early Tuesday, O'Brien said.
An autopsy is scheduled for later Tuesday.
Harrison Area detectives are investigating.
The STNG Wire contributed to this report.