Her grandmother, Eleanor Hennessy, was a huge influence in her early life. At fifteen, Jill began modeling in Toronto. Her grandmother drove her all over town.

Her father, John, was a meat salesman, which required considerable travel and resulted in frequent moves. Her mother, Maxine, left the family when Jill was small. She also has a younger brother, John Jr.

Described by Miguel Ferrer as being a non-angry version of her "Crossing Jordan" (2001) character Jordan Cavanaugh.

Voted one of the "Fun and Fearless Females" by Cosmopolitan Magazine (2002.)

Had a second marriage ceremony in January 2001 at New York City Hall with Rudolph W. Giuliani officiating.

She used to busk (play the guitar and sing for money) in the New York City subway.

Sometimes makes appearances at music events as a guest guitarist where she usually performs barefoot.

She is such a fan of the folk duo Indigo Girls that a poster of the act hangs in the kitchen set of her character in "Crossing Jordan" (2001).

She and Paolo welcomed a son, Marco, on 17 September 2003.

Finalist for role of Dana Scully on "The X Files" (1993).

Speaks Italian, French, Spanish and German

Has a song named after her: "The Ballad of Jill Hennessy" by Mollycuddle.

Barely graduated from Kitchener, Ontario, Canada's Grand River Collegiate (high school), while her twin sister, Jacqueline Hennessy, has a Master's degree in French Literature.

Her mother, Maxine, is a secretary in Montréal and a fantastic cook. Jill's father, John Paul Sr., is a meat salesman and a sales & marketing executive in Canada. She has a twin sister, Jacqueline Hennessy, who is an actress and a journalist, and a younger brother, John Paul Jr.

Loves riding motorcycles with her husband.

Has Irish, Italian, Swedish, French and Ukrainian ancestry.

She loves to cook, and opened Hennessy's Tavern in Northvale, New Jersey in 1999. The Tavern serves "comfort food."

Has a twin sister named Jacqueline with whom she used to perform in an act named (what else?) "Jack and Jill".

Shares the same three initials with Jeff Hardy, a professional wrestler of the World Wrestling Entertainment.

Expecting second child with husband Paolo Mastropietro in late 2007.

Son, Marco, born September 17, 2003.

Son Marco, born 17 September 2003.