The department said officers found Hernandez at 3:05 a.m. He hanged himself in his cell in Shirley's Souza Baranowski Correctional Center.
Personnel attempted to save Hernandez, who was transported to the UMass Memorial HealthAlliance Hospital in Leominster where he was declared dead at 4:07 a.m.
"Mr. Hernandez was in a single cell in a general population unit," a statement from the corrections department said. "Mr. Hernandez hanged himself utilizing a bedsheet that he attached to his cell window. Mr. Hernandez also attempted to block his door from the inside by jamming the door with various items."
Massachusetts State Police launched an investigation into Hernandez's death.
Hernandez began playing for the Patriots as a tight end in 2010. He was immediately released in 2013 by the NFL team after he was arrested for Lloyd's death.