Chicago police want to know if the suspect is the same person responsible for two other recent sex assaults.
The police issued a warning for women who live on the city's Northwest Side.
The latest sex assault happened in the 2100-block of North Maplewood.
Police believe the same person could be responsible for sexual assaults that happened in the 2300- block of West Moffat and 1700-block of North Marshfield.
All three sexual assaults happened right around the border of Bucktown and Wicker Park. In each case, the offender took the victim to a secluded area and escaped on foot. Because all three victims were alone when the attack happened, police are stressing the importance of paying attention to your surroundings.
"Always be aware of your surroundings, trust your instincts. If you suspect someone is following you, call 911 immediately and try to go to a safe, crowded, well-lit area," said Commander Joseph Salemme, Chicago Police.
The attack happened in the 2100-block of North Maplewood, shortly after a woman exited a nearby Blue Line station.
"I have two daughters, that scares me. Sometimes they're coming in the night. That scares me," said Hector Maisonet, resident.
Maisonet just found out about Wednesday morning's incident, as well as another sexual assault of a woman two weeks ago in the 2300-block of West Moffat. Police say it's possible the two attacks and a third sexual assault last September in the 1200-block of North Marshfield are related.
The offenders are unknown but police released an image of the man they say is responsible for the attack on the second of three community alerts issued by investigators.
"The offender is these incidents described as a male, black, 20 to 30 years of age, 5'6" to 5'8", 180 to 200 lbs., black hair, brown eyes, and a goatee. He is medium to dark complected and is armed with a knife," said Commander Salemme.
All three women are in their early 20's and were walking alone in the early morning hours when they were attacked. In Wednesday morning's case, the woman was wearing headphones and a hoodie. Investigators urge everyone to pay attention to his or her surroundings.
As far as the police investigation goes, detectives would not specify if they have patrols in the area and would not also say if they have a good idea of who the offender. But they encourage anyone with information about the attacks to give Area 5 police a call.