Police say the suspect approaches his victims from behind and forces them into isolated areas at gunpoint.
Wednesday's alert is the third warning police have issued since the attacks were first reported back in October. Three of the attacks happened this year.
Chicago police say that since October, eight sexual assaults have taken place in an area bounded by 115th street, the Little Calumet River, Normal Avenue and Ashland Avenue.
The most recent attack happened on February 14 in an alley near 120th and South Union. The 18-year-old victim in that attack says she was walking alone when a man pulled a gun, sexually assaulted her and threatened to kill her if she called for help.
It's not known if the assaults are connected to ones that have taken place in the south suburbs, such as Harvey, Dixmoor and Ford Heights.
Three assaults have happened in suburban Riverdale and police released a sketch of a possible suspect.
Meanwhile, Chicago police are cautioning people to be careful of their surroundings when they're out and about, which is something some residents have taken to heart.
"If you travel in one, of course you might get targeted, but travel in two's or more and then that will be a harder target," said Pauline Neal, resident.
"I think it's terrible. The neighborhood wasn't that bad, but I guess it's getting worse. Maybe it needs to be more police or somebody out there to try to stop that," said Christian Carter, resident.
"If we gotta come together as a community to catch this guy, then we're gonna do what we need to do. I'm not talking about harming anybody, because that's in the law's hands and God's hands, but we gotta get this dude off the streets," said Sidney Jones, resident.