Williamson, who hails from Spartanburg, South Carolina, also had the in-state Gamecocks and Clemson among his top choices.
"Duke stood out because the brotherhood represents a family," Williamson said. "Coach K (Mike Krzyzewski) is just the most legendary coach that ever coached college basketball. I feel like going to Duke University, I can learn a lot from him."
Duke now has commitments from the three top-rated players in the ESPN 100, with No. 1 R.J. Barrett and No. 3 Cam Reddish joining Williamson in Durham. The Blue Devils also have a commitment from No. 10 Tre Jones.
Duke is the first program to gain commitments from each of the top three recruits in the same class in the ESPN 100 era (since 2007). Per ESPN Stats & Information, Duke now has landed 11 top-three recruits in the ESPN 100 era. Kentucky and Kansas are next on the list, landing four apiece.
This is also the second consecutive season Duke has landed four players ranked in the top 10 of the ESPN 100.
"I feel like we can all do something special," Williamson said.
Duke is expected to lose most, if not all, of its starting five after this season. Grayson Allen is a senior, while Marvin Bagley III, Wendell Carter Jr. and Trevon Duval are all projected first-round picks.
While Williamson's dunking ability and jaw-dropping athleticism are his best attributes, he's more than that. The 6-foot-6, 275-pound power forward is built like a tight end, but he combines that strength and physicality with quick feet and adept passing ability.
Williamson is still at his best in transition, though, and will need to get in better shape and improve his shooting ability to dominate at the next level.
Williamson thanked both Clemson and South Carolina for their recruitments.
"I love my state to death," he said.
Williamson has built a massive social media presence, with his 1.1 million Instagram followers and close to 100,000 Twitter followers. Drake wore his jersey in an Instagram post.
"It's fun, and it can be not-so-fun at the same time," he previously has said of the attention. "It's fun because, going all over the world, I was in Italy and people were asking me for pictures, 'Are you Zion? I don't believe you're in Italy right now. This is crazy.' I tell [people] my name, and they go, 'Oh my god, it's really you.' That part's fun. People knowing who I am."