The woman was working at the drug store located at 1372 N. Milwaukee Ave. when an unknown person approached her just after 9:30 a.m., police said.
The individual stabbed the victim multiple times and left the store, police said. The woman was pronounced dead at the scene.
The victim has been identified as Olga Maria Calderon of Chicago, according to the Cook County Medical Examiner's Office.
Flowers lie outside the doors of the still-shuttered Walgreens where Calderon was working the register Sunday.
It is still unclear whether the stabbing was a targeted attack or a random act of violence. As police question a person of interest, they still have not released any details on a possible motive.
Regular customer Robert Szabla said Calderon was joking around with him about 10 minutes before she was killed when he went there to make a purchase.
"She said, 'Oh I hope it's not gonna be any robbery today because it's raining and they are afraid of rain,'" Szabla said.
WATCH: Police describe possible suspect in at Wicker Park Walgreens stabbing
While police have said the store was not robbed this time, some in the neighborhood said the Walgreens is a frequent target of robberies.
"I myself witnessed it several times," Szabla said. "Alcohol, cosmetics. People just walk in, take things and they walk out and these employees cannot do anything."
Police said this is the second time this month, this particular Walgreens has been targeted by a knife-wielding offender. Just five days ago, police said the store was subject to an armed robbery.
While police said nothing was taken during the stabbing, they are looking for any links.
Crisis responder Andrew Holmes said the woman who was killed is the mother of a 3-year-old boy and an 11-year-old girl. Her family is struggling to come to grips with the loss.
WATCH: Police investigate murder at Wicker Park Walgreens
"Her daughter is taking it really hard," Holmes said. "The younger baby doesn't understand yet what's actually happened, but the daughter, she knows."
Walgreens spokesperson Jim Cohn said in a written statement: "We are very saddened to learn of this tragic incident, and extend our deepest condolences, thoughts and prayers to the family and loved ones of our team member. The safety of our customers and team members is our top priority, and we're continuing to work with local authorities in their investigation. We are also making counseling and other resources available to our other store team members at this location."
ABC7 has reached out to Walgreens to confirm if the store has been a regular target for thieves, but has not heard back.
Charges are still pending in the case. Police said that even if there is enough evidence to go forward, charges likely won't be filed until Tuesday because of the holiday.
Anyone with information is asked to call (312) 746-5446 or visit home.chicagopolice.org.