The incident happened on the bike path at about 10:30 a.m. on a stretch of trail between Brandon and Larkin Avenue south of Interstate 80, between the Joliet and Rockdale area.
"This happened in the middle of the day," said State Police Master Sergeant Jeffrey Padilla. "We're very concerned. We're working to try to develop more information on who our suspect is."
The jogger told police that she was jumped by a man hiding in the bushes, threatened with a knife and assaulted. The woman was found by another jogger who walked her to the Rockdale Police Department a few blocks away.
The suspect was described as a Hispanic male with a heavy accent in his late 20s to early 30s. He is described as being between 5-feet-8-inches and five-feet-10-inches tall. He was wearing dark sweatpants, a white t-shirt and a long sleeved orange shirt.
A police sketch artist is schedule to meet with the victim Tuesday.
Meanwhile, conservation police patrols have increased along the trail. On Monday, not many people were on the path and those who were enjoying the trail said they don't run alone.
"I used to feel safe until I heard about this," said jogger Maritza Diaz. "I always come with a friend. You have to be safe about that stuff, be cautious."
"It's a shock," said Tim Ciancanelli. "It's a pretty popular place on the weekends. For something like this to happen in the middle of the day, it's pretty bizarre."
Anyone with information is asked to call Illinois State Police at 847-722-2865.