Family
- grandfather John Nicholson: An itinerant alcoholic whom Nicholson believed was his father until a Time magazine researcher revealed otherwise while preparing an Aug. 12, 1974 cover story on the star; he never learned his father's true identity
- grandmother Ethel May Nicholson: Raised Nicholson as her son; he believed her to be his mother until he was 37 years old (she had already died)
- mother June Nicholson: Spent a decade in chorus lines before marrying Murray Hawley, but when he left her, returned to her family in Neptune City, NJ; diagnosed with cervical cancer at age 43 (c. 1962) and died without telling Jack she was his mother; he had always believed she was his older sister
- aunt Lorraine Nicholson: Nicholson believed her to be his older sister; according to Lorraine, Jack had learned the truth prior to the Time cover story of Aug. 12, 1974 from a 15-page letter written by a man purporting to have fathered him with June; Lorraine told Jack that the man was only one of the suspects June had dated at the time
- half-sister Pamela Hawley Liddicoat: Born c. 1946; daughter of June Nicholson; was murdered in February 1994
- daughter Jennifer Nicholson: Born c. 1964; mother, Sandra Knight; worked as design assistant on "The Two Jakes" (1990); featured in the Nicholson-financed film, "Blue Champagne" (1991); gave birth to Nicholson's first grandson Sean on February 20, 1996; married Mark Norfleet on August 31, 1997
- daughter Lorraine Broussard Nicholson: Born April 16, 1990; mother, Rebecca Broussard
- son Raymond Nicholson: Born Feb. 20, 1992; mother, Rebecca Broussard
Companions
- Companion Michelle Phillips: Lead singer of the popular 1960s group "The Mamas & the Papas"; later took up with Warren Beatty
- Companion Winnie Hollman: Danish; dated early 1980s; rumored to have had a daughter, Honey Hollman (born 1981) with Nicholson; this has never been publicly acknowledged by Nicholson
- Anjelica Huston: had on-again, off-again relationship from c. 1973 until 1990
- Lara Flynn Boyle: had on-again, off-again romantic relationship from summer 1999
- Mimi Machu:
- Rebecca Broussard: born c. 1963; met while she was waitressing at Helena's in Los Angeles, a restaurant in which Nicholson was an investor; played Nicholson's secretary in "The Two Jakes"; featured in "Blue Champagne" (lensed 1991), "Cannes Man" (1996) and "Point of Betrayal" (1996); married to record producer Richard Perry from 1987 to 1989
- Susan Anspach: co-starred in "Five Easy Pieces"; no longer together; she alleges that together they had a son, Caleb, who was born on September 26, 1970; claims have been made that Nicholson privately acknowledged the child but has refused to do so publicly
