The Illini (2-0) never trailed, jumping out to a 12-1 lead in the first five minutes of the game and leading 40-27 at the half. Junior guards Rayvon Rice and Tracy Abrams each scored 13 points.
Nnanna Egwu and Jaylon Tate each added 10 points for Illinois. Egwu also blocked five shots, tying his career high. The Illini blocked 11 shots in the game, the most under second-year coach John Groce.
The Gamecocks (0-2) were led by senior guard Brian Williams, who scored 12. Senior forward D. J. Felder grabbed 10 rebounds to lead Jacksonville State. Sunday's game was only the third game Jacksonville State had played against a Big Ten opponent in school history, losing to Michigan State in 2002 and Nebraska last year.
Felder and junior guard Darion Rackley each scored 10 points for Jacksonville State.
Illinois started the second half 0 for 6 from the field, including a missed dunk by 6-11 center Nnanna Egwu, before settling down. The Illini didn't commit a turnover in the second half, and played all 11 available players throughout the game, often substituting three and four at a time.
Jacksonville pulled to within 40-33 at 16:34 of the second half on two three-pointers by Williams, who ended up 2-5 from beyond the stripe.
Illinois shot 52 percent from the field (32-61) while Jacksonville shot only 33 percent (23-70). The Illini also outscored the Gamecocks 40-28 in the paint, led by Egwu's 5 of 8 shooting and some aggressive play inside by Illinois' big men.
Sunday's win marks the 14th straight season the Illini have started the season with at least two straight wins. Illinois has also won 24 straight home games against non-conference opponents, dating back to the NIT tournament in 2010.
Jacksonville travels to Chicago State on Tuesday while Illinois hosts Valparaiso on Wednesday.