On April 11, 2016, Jackson tweeted that he would be attending the University of Kansas in Lawrence, Kansas to play basketball, picking KU over Michigan State and Arizona. During his only season at Kansas, Jackson showcased his all-around play between scoring, rebounding, play-making, and defending. Although he started as a power forward for the Jayhawks, not Jackson's normal positions of both small forward or shooting guard, he still recorded 16.3 points, 7.4 rebounds, 3.0 assists, 1.7 steals, and 1.1 blocks per game with the team in his freshman season. As a result of his efforts, he was named as an All-Big 12 First Team member, the Big 12 Freshman of the Year, was named as a second-team All-American according to Sporting News, and was also considered a third-team All-American according to the Associated Press and National Association of Basketball Coaches. On April 17, 2017, Jackson officially declared for the 2017 NBA draft and hired former Chicago Bulls point guard B. J. Armstrong as his agent, officially forgoing his remaining college eligibility.