Katie Borenstein was found at The Edge apartments in downstate Normal around 5:20 p.m. Saturday.
Borenstein attended high school in northwest suburban Buffalo Grove and was found dead at the scene by police in the 800 block of Hovey Avenue, according to Normal Police Sgt. Nick Thacker.
An autopsy Monday found she died of a pulmonary artery blood clot. Borenstein was not a current student at ISU, police said.
Police say Borenstein's death is unrelated to an ISU student death in Bloomington. Investigators say student Yusuf Jamal Ahmad "Yoshi" Ziada's body was found in an empty field less than three miles from the university's campus Sunday morning.
McClean County Coroner Beth Kimmerling said the young man from Oak Lawn was not dressed properly for the weather conditions, adding that he had no coat, no hat nor gloves. His preliminary autopsy results indicate that he had signs and symptoms of cold exposure
The 7 a.m. temperature in Bloomington was 23 degrees, with a wind-chill index of 7 above, according to the National Weather Service.
Police say early information suggests that Ziada wandered away from The Chateau Hotel on Jumer Drive in Bloomington, approximately three miles from ISU's campus, and then collapsed; he has no external injuries that led to his death, the coronoer said.
Toxicology tests are pending on both victims.
The Sun-Times Media Wire contributed to this report.