Shares his birthday with Marla Sokoloff, Alyssa Milano, Jennifer Beals and Édith Piaf.
He appeared in a 1994 episode of "Homicide: Life on the Street" (1993) that was directed by his father, Steven.
Ranked #48 on Premiere's 2006 "Power 50" list. It is his first appearance on the list.
On Phantom Planet's album "The Guest", lead singer Alex Greenwald lists him in his thank yous. Alex appeared with Jake in Donnie Darko (2001).
Was personally approved by Joe Namath to play the football legend in an upcoming biopic about the latter's life.
Had his Bar Mitzvah party at a homeless shelter, something his parents encouraged to help him recognize how privileged his own childhood had been (a Bar Mitzvah is the coming-of-age service that Jewish boys celebrate at age 13).
His first four big roles were in movies with alliterated titles: Bubble Boy (2001), Donnie Darko (2001), Moonlight Mile (2002), The Good Girl (2002).
Voted #10 in Elle (France) Magazine's "15 Sexiest Men" poll (June 2007).
Received his first driving lesson from Paul Newman.
As of 2007, has starred in three movies where he played not only a real person, but the person who wrote the book upon which the film was based: Homer Hickham (October Sky), Anthony Swofford (Jarhead) and Robert Graysmith (Zodiac).
Uncle of Ramona Sarsgaard, born October 3, 2006. She is the daughter of his older sister Maggie Gyllenhaal and Peter Sarsgaard.
Dropped out of Columbia University after two years (2002).
Auditioned for and was one of the top contenders for the role of Batman/Bruce Wayne in Batman Begins (2005).
He gave Kirsten Dunst a gray and white kitten for her birthday. She named the cat Sophie.
Godmother is Jamie Lee Curtis.
His last name is pronounced Jill-en-hall.
Like all Gyllenhaals on the male line, he is a Swedish nobleman by birth right and is listed in the Swedish Almanac of Nobility ("Sveriges Ridderskaps och Adels Kalender" in Swedish).
Godfather is Paul Newman.
Played brother to real life sister Maggie Gyllenhaal in their movie Donnie Darko (2001).
Very good friends with actress Jennifer Aniston.
Campaigned for the Democrats in the 2004 US election.