Sullivan was a junior at Notre Dame University. He died last Wednesday when the portable lift he was filming on toppled to the practice field.
Sullivan's younger sister, who is a freshman at Notre Dame, and brother spoke at the funeral Monday at St. Mary's Church in Buffalo Grove.
"This is a special time that we have to come together as a community and support the family," said Bill Ferreira, family friend.
Sullivan is from Long Grove. Friends from Carmel Catholic High School and classmates from Notre Dame attended the Mass.
"He died doing what he loved. It's unfortunate that we're not going to have him around, but at the same we loved having him as long as we did," said Michael Miley, uncle. "Sometimes when you say a kid tells stories that means something kind of funny, but he loved to tell stories. Sometimes he was on the other side of the cameras."
Coach Brian Kelly also attended the funeral. He has taken responsibility for holding practice outdoors during a high wind advisory on the day of the accident.
After the funeral, the family held a private burial. His parents issued a written statement that said "Declan felt privileged to have a role with the football program videotaping games and practices."
Indiana regulators are investigating whether Notre Dame violated safety rules by allowing Sullivan onto the lift.