Is good friends with 1013 Productions' Chris Carter, having appeared in most of his work: as a guest star in two episodes of The X-Files (1993), a supporting role in The X Files (1998) and recurring roles on Harsh Realm (1999) and Millennium (1996).
Grew up in Newberry, Michigan and was raised Roman Catholic.
He elongated his last name to "O'Quinn" from his real name of "Quinn" to distinguish himself from another person named Terry Quinn already acting in films.
Has been balding since his early 20s and has appeared with a partially or entirely shaved head in most of his films.
Has been experienced in percussion since high school.
Has had roles in both of J.J. Abrams's hit television series Alias (2001) and Lost (2004).
Not many know that he is a talented guitarist and singer. He is a particularly big fan of Neil Young and can apparently do a dead-on impression of him.
Although always friendly onset, he keeps private and mysterious habits apart from his younger Lost (2004) co-stars, who often get together for wild parties when not shooting. He keeps this enigmatic aura so they will regard him similarly to the way they regard his mysterious character Locke.
Is one of the few cast members of Lost (2004) who did not have to audition, because his former collaborator (from Alias (2001)) J.J. Abrams thought of O'Quinn for the part of Locke before the actor was even offered it.
Has two sons: Oliver Quinn (b. 1984) and Hunter Quinn (b. 1986).
Attended and graduated from the University of Iowa in Iowa City, Iowa.
Attended and graduated from Central Michigan University in Mount Pleasant, Michigan.
In an episode of Lost (2004), his character Locke's parents were played by Kevin Tighe and Swoosie Kurtz, who are both only eight years O'Quinn's senior.
Has appeared in episodes of two different series with the same name. Both Millennium (1996) and Lost (2004) have had episodes featuring O'Quinn called "Walkabout".
Has an Irish Terrier named Reggie.
Was the chief architect for the infamous "Locke" baseball field designed mostly in part for the Three Village Little League.
Actually learned how to properly throw and handle knives for his role on Lost (2004).
His brother Thomas Anthony Quinn is also an actor, who acts and teaches theatre in central Illinois.
He is one of eleven children.
Has English and Irish ancestry.
Although he played Chris Nash's father in Mischief (1985), he is only nine years his senior in real life.