Grandison began his college career at
Holy Cross, where he played in all 31 games and started 18 games his freshman year. During his first year, he averaged nine points a game and led his team in scoring six times and rebounding nine times. As a sophomore, Grandison started in all 33 games. He led the team in scoring with an average of 13.9 points per game, which was 11th in the
Patriot League, and was second on the team in rebounding with five rebounds per game. Along with this, Grandison shot 36.5 percent from three with a team high of 69 three-pointers, which was eighth in the Patriot league. Some individual highlights for the season included scoring a double-double of 21 points and a career-high 10 assists against
Stony Brook on November 16, 2018, a career-high of 25 points against
Iona on December 30, 2018, and a double-double of 22 points and a career-high 16 rebounds against
Lafayette on March 5, 2019. After sitting out the 2019–20 season because of NCAA transfer rules, Grandison started his Illinois career as a bench player. However, after Illinois suffered consecutive losses to
Maryland and
Ohio State, Coach
Brad Underwood decided to shake up his lineup and put Grandison in the starting lineup for their game against
Penn State on January 19, 2021. This proved to be a successful change as Illinois beat the Nittany Lions 79–65, and Grandison started 15 of the final 16 games of the season. and won the
2021 Big Ten men's basketball tournament. For the entire season, Grandison averaged 4.6 points and 3.4 rebounds a game. For his senior season, Grandison saw a more increased role as he started in 23 of the 30 games he played. On February 19, 2022, Grandison had his most points as an Illini with 24 points and tied a career-high in three pointers made in a game with six as he helped lead his team to a win against
Michigan State 79–74. Despite this, he averaged 9.6 points and 3.8 rebounds per game, which was fourth on the team for both, and earned an Academic All-Big Ten selection. After graduating from Illinois, Grandison decided to use his final year of eligibility and transferred to Duke. While attending Duke, Jacob was selected to the All-ACC Academic Team. ==Professional career==