It happened as officers were pursing suspects in a double murder.
The officer suffered non-life-threatening wounds.
Police say one suspect is dead Saturday night and two others are in custody, but not before they opened fire on a police squad car.
Chicago police are gathering evidence at three separate crime scenes on Saturday night.
The first is at an apartment building in the 5800-block of North Winthrop. Members of the Chicago police gang investigation unit had been outside on a stakeout as part of a narcotics-related homicide investigation.
"The officers observed the subjects running from the building. A call of 'Shots fired' came out. The officers entered the building. They discovered three victims, two DOA and one in critical condition," said Superintendent Jodi Weis, Chicago Police Department.
The violence continued a short time later near Thorndale and Broadway as the suspects encountered another officer.
"The offenders fled ramming a marked squad car. They fired after police, striking one of our officers," Weis said.
The wounded officer was shot in the leg and police have not released his name. They only say he's a 39-year-old, 12-year veteran of the force.
He was taken to St. Francis Hospital and is in good condition Saturday night.
"I think this again is a stark reminder of the dangers our men and women face every day. They are out there risking their lives every day and this is just what happens but he's going to be fine," Weis said.
Police continued to pursue the suspected vehicle, believed to be this black Ford pickup, as its occupants fired more shots at officers.
The chase ended near Devon and Greenview avenues.
Police say one suspect was killed and two more are in custody.
"I guess he was shot before they pulled him out of the truck because by the time I walked down there, the ambulance was coming to put him in the stretcher," said witness Brittany Rolling.
"There's 20 police cars, and they started blocking off the intersection, and it was very frightening," said witness Marc Wright.
Police are not releasing details about the circumstances surrounding the death of the one suspect and the other two found dead in the 5800-block of North Winthrop.
They do not believe there are other offenders involved in this violence that are still at large.