was born in San Jose, California, on December 5, 1947, the youngest of three children. He grew up in Santa Clara before his family moved back to San Jose to take advantage of cheaper housing. While growing up, Jim delivered newspapers and did other odd jobs to earn pocket money, but still had plenty of time for football.

A passing quarterback in junior high school, Jim went on to a stellar career as a quarterback for James Lick High School in San Jose. As a senior, he led his team to an unbeaten season, and played in the state all-star game. Heavily recruited by several major colleges, he chose Stanford primarily because of its excellent academic program.

Plunkett's first year at Stanford was seriously hampered (both physically and academically) by surgery for a benign neck tumor, which he underwent in August 1966. After a far-less-than-stellar freshman year, head coach John Ralston suggested that Plunkett become a defensive end. When Plunkett refused, Ralston redshirted him for the 1967 season. But Plunkett wasn't deterred. In 1968 (his official sophomore year), he threw for 14 touchdowns and set a Pac-8 record with 2,156 yards passing. In 1969, he set Pac-8 records for touchdown passes (20), passing yards (2,673), and total offense (2,786 yards), and ranked third nationally in total offense and fifth in passing. In 1970, he passed for 2,715 yards and 18 touchdowns, leading the Indians to an 8-3 record and a Pac-8 championship. His achievements that year led to his being awarded the 1970 Heisman Trophy (over Joe Theismann and Archie Manning). He then led his team to a 27-17 victory over previously unbeaten Ohio State in the 1971 Rose Bowl, completing 20 of 30 passes for 265 yards and one touchdown. By the end of his three-year college career, Plunkett had set NCAA records for most yards total offense (7,887) and most passing yards (7,554).

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