Crystal Lake police said they were called at about 5:32 a.m. to a report of two people possibly asleep in a car in the 700-block of Coventry Lane.
A woman, 20, and a man, 31, were found "unresponsive and with no obvious signs of injury," police said.
Both died at the scene, Crystal Lake police said.
The McHenry County Coroner identified the victims as Yeisimar Morales-Sanchez of Crystal Lake and Kirby Graham, of Grayslake.
No other information regarding the investigation was released.
The cause of death had not been released.