The St. Croix County sheriff's office was called to the crash around 5 a.m. Sunday in the Town of Hammond. Deputies found no one in the car.
Authorities say emergency responders searched the area and found the body of 38-year-old Kristelle Wolle in nearby Pine Lake.
Sheriff's Capt. Jeff Klatt tells the St. Paul Pioneer Press that Wolle may have walked into the lake after the crash.
Authorities don't know yet what killed her. The Ramsey County medical examiner's office is conducting an autopsy.