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Early life and education

John Joseph Nicholson was born on April 22, 1937, in Neptune City, New Jersey, the son of a showgirl, June Frances Nicholson (stage name June Nilson; 1918–1963). Nicholson's mother was of Irish, English, German, and Welsh descent. Nicholson has identified as Irish, comparing himself to the playwright Eugene O'Neill, whom he played in the film Reds: "I'm not saying I'm as dark as he was... but I am a writer, I am Irish, I have had problems with my family." His mother married Italian-American showman Donald Furcillo (stage name Donald Rose; 1909–1997) in 1936, before realizing that he was already married. Biographer Patrick McGilligan stated in his book Jack's Life that Latvian-born Eddie King (originally Edgar A. Kirschfeld), June's manager, may have been Nicholson's biological father, rather than Furcillo. Other sources suggest June Nicholson was unsure of the father's identity.

As June was only 17 and unmarried, her parents agreed to raise Nicholson as their own child without revealing his true parentage, with June acting as his sister. In 1974, Time magazine researchers learned, and informed Nicholson, that his "sister", June, was actually his mother, and his other "sister", Lorraine, was really his aunt. By this time, both his mother and grandmother had died (in 1963 and 1970, respectively). On finding out, Nicholson said it was "a pretty dramatic event, but it wasn't what I'd call traumatizing... I was pretty well psychologically formed".

Nicholson grew up in Neptune City, New Jersey. Before starting high school, his family moved to an apartment in Spring Lake, New Jersey. "Nick", as he was known to his high school friends, attended nearby Manasquan High School, where he was voted "Class Clown" by the Class of 1954. He was in detention every day for a whole school year. A theatre and a drama award at the school are named in his honor. In 2004, Nicholson attended his 50-year high school reunion accompanied by his aunt Lorraine.