There have been 1,052 players in MLB history born in Illinois (or at least that’s how many we know of). And of those players, the one with the most home runs is… Jim Thome with 612. But the player who’s second; the player who had the “record” prior to Thome was Gary Gaetti with 360.
Gary Gaetti homered in his MLB Debut (in his first at-bat) on September 20, 1981 for the Twins. As a rookie the following season he hit 25 long ones. He was a mainstay at the hot corner for the Twins in the 1980s, winning four Gold Gloves (1986-89) with two All-Star selections (1988-89).