Williams announced his decision Tuesday on Twitter and Instagram. The 6-foot-4, 220-pound defender also considered Alabama, Clemson and Georgia.
"It's been long, it's been hard, but I stand ten toes for whatever it takes to be great," Williams wrote Tuesday on social media. "Changing my mind and refocusing on my senior year."
Williams is a dynamic defender and has lined up at safety, cornerback, linebacker and edge rusher.
The Hurricanes were just outside the top-10 among recruiting classes for 2021 before Williams' commitment. Miami now has eight commitments from the 2021 ESPN 300.
The Hurricanes also have commitments from No. 102 Jacolby George, No. 140 Romello Brinson, No. 155 Savion Collins, No. 165 Laurence Seymore, No. 197 Jabari Ishmael, No. 229 Thad Franklin and No. 298 Michael McLaughlin.
All eight of those commitments are from Miami-Dade County or Broward County.
Williams attends American Heritage School in Plantation, Fla., which is about 17 miles from the Hurricanes' home field, Hard Rock Stadium, and 36 miles from their Coral Gables, Fla., campus.
The Hurricanes hired Diaz last off-season and posted a 6-7 record in 2019. They are scheduled to start the 2020 season against Temple on Sept. 5 in Miami.