Okongwu, a 6-foot-8 Chino Hills (Calif.) product, chose the Trojans over UCLA and Arizona State.
"I just wanted to rock with USC," Okongwu told ESPN. "It's in L.A. I wanted to stay home. I really connect with their coaching staff. They recruited me the hardest and USC feels like home to me."
Ranked No. 15 in the ESPN 60, Okongwu slots in as the No. 3 power forward in the 2019 class. He has a 7-foot-plus wingspan, and averaged 14.5 points, 8.3 rebounds and 2.3 blocks last summer for Compton Magic on the Adidas circuit. More recently, Okongwu led Chino Hills to a state title and earned Mr. Basketball in the state of California.
"I think I'll fit in well at the power forward spot," Okongwu said. "They'll use me as a big and they'll develop me into a more versatile [player]. They practically play positionless basketball."
Okongwu is USC's first commitment in the 2019 class, although the Trojans are also expected to land ESPN 60 forward Isaiah Mobley.
Trojans coach Andy Enfield hired Eric Mobley, the father of Isaiah and 2020 prospect Evan Mobley, as an assistant coach in late March. Mobley had also been a coach in the Compton Magic program.