DeJean was a four-year football letterman as a quarterback and defensive back at OABCIG high school in Ida Grove, Iowa. He holds school records for pass completions and passing yards in a season, career passing yards and career passing touchdowns. He also lettered three years in baseball, basketball, and track. In his senior season, he was named to the Des Moines Register Elite All-State team and committed to Iowa at the beginning of the season.
In 2021 as a freshman, DeJean saw action in 7 games, mostly on special teams and was named the Next Man In Award for his play.
DeJean started 2022 listed as a second-team “Cash” linebacker and strong safety. He started at cornerback for 10 games and outside linebacker for 3. He had a strong season, totaling 56 tackles and 5 interceptions and returned 3 of the interceptions for touchdowns. He averaged 16.5 yards per punt return for the Hawkeyes and his outstanding season led him to be named first-team All-Big 10.
DeJean was named a Draft 412 pre-season first team All-American heading into the 2023 season.
In 2023, DeJean started 10 games for Iowa and suffered a lower leg injury late in the season. He collected 41 tackles and picked off 2 passes for the Hawkeyes.