The inside linebacker signed paperwork amongst fellow Irish football players to head to Missouri Western as a preferred walk-on next season.
Pettijohn battled injuries during his senior season at Lafayette, but was a captain and leader on a squad that posted a 7-5 record and a trip to the district championship.
He'll join a program that's won 20 games and the conference title in the last two seasons.
"In the past couple years, the Griffons have grown and grown," Pettijohn said. "I feel like they're just going to continue to grow and grow, and I want to be part of that."
Other former Lafayette Fighting Irish currently on the Missouri Western football team include Austin Drennen, Kenny Grant and Travis Webster.