Thornton, 6-feet 3-inches and 250 pounds, had 17 catches for 230 yards and 2 touchdowns last season, before a knee injury forced him to miss the season's final three games.
He raised his value in the draft with a fine performance in the Hula Bowl last January, said Gene Murphy, Fullerton coach.
"I was too nervous to watch it (the draft) on television," Thornton said. "I got a call and they asked me what I thought of the Chicago Bears. I told them I liked the team and the caller said that was good because I was just drafted by them."
Thornton came to Fullerton from Analy High School in Sebastopol, Calif. where he played quarterback. His first season at Fullerton he was a quarterback but didn't play. He switched to tight end as a sophomore.
He finished his career at Fullerton with 48 catches for 571 yards and 5 touchdowns.