The crash happened early Saturday in northwest suburban Prospect Heights.
The Cook County Medical Examiner identified the victims as Elibeth Solis, 16, of Park Ridge; Jessica Ferrer, 15, of Arlington Heights; and Freddy Najera, 16, of Mount Prospect.
The medical examiner performed autopsies on the teenagers Sunday and said all of them died of multiple injuries caused when the car struck a fixed object. A fourth teen survived the crash.
Toxicology tests will be done to determine if drugs or alcohol were involved. Police say the car was going at a high rate of speed when it crashed.