Drowning was the cause of death, according to the Ramsey County medical examiner's office.
The teen is believed to have jumped from the Stone Arch Bridge last week with his girlfriend, 16-year-old Erika Borgstrom.
Both were students at St. Croix Central High School in Roberts, Wis. and were last seen on the evening of May 10, KSTP reported.
The Hennepin County Sheriff's Office said witnesses saw the two jump from the bridge around 4:30 a.m. on Tuesday, May 14. Both were presumed drowned.
Borgstrom's body has not been found.
WCCO said this is the third suicide incident the high school has dealt with this year.