The officer was on-duty around 1:31 a.m. when she went to the Wendy's drive-thru at 1623 W. Division St., according to Chicago police.
As she began to eat, the officer discovered hair and dirt in her food, police said.
The officer went into the restaurant and talked with an employee who was dismissive of her complaint, according to CPD.
The officer declined medical treatment.
No one is in custody as Area Three detectives investigate.
On Tuesday, Wendy's released the following statement: "The quality and integrity of our food is our number one priority and we take any food-related claims extremely seriously. We have been in touch with representatives from the Chicago Police Department and will fully investigate this matter. We have great respect for law enforcement and their service to our communities."