The incident took place in the 5600-block of West Leland Avenue in Jefferson Park.
Just after 2:20 p.m., an off-duty detective assigned to the Area Four Detective Division saw the woman being attacked, and fired shots at the suspect, police said.
The detective suffered a graze wound to the leg, while trying to stop the suspect, police said.
The suspect remains at large Tuesday evening.
The detective was taken to Lutheran General hospital in fair condition after the incident, Chicago fire officials said.
The woman was taken to Ascension Resurrection hospital in very critical condition, CFD said.
She later died, the Cook County Medical Examiner's Office said.
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A worker nearby, who did not want to be identified, said the suspect was seen running from the scene.
The worker said he heard four gunshots.
CPD sources said the attack did not appear to be random.
Crime scene tape and a police presence were still visible about 6 p.m.
The Chicago Civilian Office of Police Accountability is responding to the incident, and the Investigative Response Team is also on the scene investigating.
The officer involved will be placed on routine administrative duties for a minimum period of 30 days.
Anyone with information is asked to call COPA at 312-746-7608 or visit www.chicagocopa.org.
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