The victim was found Monday afternoon along a bike path in the Poplar Creek Forest Preserve in unincorporated Kane County near Elgin near the Fox River Water Reclamation District treatment plant.
The 46-year-old woman was taken to Sherman Hospital in Elgin.
Authorities were called to the path near Raymond Street about 12:33 p.m. Monday on a report of a person found there.
"One of our operations crew were mowing the grass in the area and observed a woman laying in the bushes off to the side here. She was semi-responsive. They called the ambulance. One of our officers is interviewing her at the hospital right now, and it appears we're investigating a sexual assault at this point," said Chief Michael Gillosfo, Kane County Forest Preserve Police. "She was not bicycling. Again, this is a preliminary investigation, (but she) met someone at another location and somehow wound up over here sometime last night, early morning hours."