Nicholson ni a bi ni April 22, 1937, ni Neptune City, New Jersey, ọmọ ti a showgirl, June Frances Nicholson (orukọ ipele June Nilson). Nicholson ká iya wà ti Irish, English, ati German ìbí. O si fẹ Italian-American showman Donald Furcillo (orukọ ipele Donald Rose) ni 1936, ṣaaju ki o to mọ pe o ti wà tẹlẹ iyawo. Biographer Patrick McGilligan so ninu rẹ iwe Jack ká Life wipe Latvian-bi Eddie King (ni akọkọ Edgar A. Kirschfeld), June ká manager, le ti ni Nicholson ká biological baba, dipo ju Furcillo.
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