The shooting took place just after midnight in the 6000-block of South Hermitage.
On Monday night, officers in the 7th District, where Valadez served, held a prayer service in his honor.
"He was really a dedicated public servant and i'm really proud of his service to the community," said Commander Keith Calloway, Chicago Police Department.
Alejandro Valadez comes from a family of police officers.
Superintendent Weis says he was on life support and was pronounced dead on Monday afternoon.
"At 2:40 on Monday afternoon, our officer was pronounced dead. His name is Alejandro, but he goes by Alex Valadez," said Supt. Weis.
It's been an all-day vigil at Stroger where police officers, family, and friends gathered to hear the latest about the 27-year-old police officer.
"They responded to a call of shots fired. He and his partner were on the scene. At that time a vehicle drove by and fired rounds in their direction. That's when he was hit. He was struck, I believe, once in the leg and once in the head," said Weis.
Chicago Police Superintendent Jody Weis would not say if the officer was a target.
The shooting happened just outside Samantha Washington's home.
" I heard the shots and made sure my sister was OK," said Samantha Washington, officer's neighbor.
"It's like everybody just got punched in the stomach. You walk around the hospital, there's young officers, they're in tears. Many do not have a lot of time on the job and now they realize how dangerous it is," said Weis.
Valadez lived on the southwest side near Midway Airport and comes from a family of police officers.
"He was a good neighbor. Always he said hi, how are you, and when I heard the news I feel so sad," said Julia Gonzalez, officer's neighbor.
Valadez is the first officer killed in the line of duty this year. Superintendent Jody Weis says he will be donating his organs and as for the investigation he said they have several leads but would not comment on whether anybody is in custody.
Valadez's fiancee was also an officer 7th district. ABC7 has learned that she is pregnant.