Deputy Police Chief Rodney Johnson told the Detroit News that Jayvon Felton died Monday at Children's Hospital.
Jayvon was diagnosed in April 2013 with leukemia. He stopped going to school, getting tutoring at home instead.
But on Jan. 31, he got his wish to become a Detroit police officer. He was given a SWAT team uniform and taken to police headquarters in a helicopter, where he was greeted by officers and by his schoolmates from Roberto Clemente Academy.
Jayvon was sworn in as chief. He told the crowd to "take the day off."
His mother, Amanda Clinkscales, thanked the department for "this very happy day."
"This ... humbles even the most hardened police officers, and reminds us why we do what we do every day, and how important every precious moment is," Police Chief James Craig said at Jayvon's swearing-in.