He made the announcement Wednesday on Instagram.
"I dreamed of playing in the league ever since I can remember. I looked up to my dad, and watched what he did and all he accomplished," Winfield wrote. "Seeing what he was able to do empowers me to say: It's my time."
His father, Antoine Winfield, played for Ohio State and spent 14 seasons in the NFL as a defensive back.
Winfield Jr. had 85 tackles this season with 7 interceptions and a touchdown.
The 5-foot-10, 205-pound Winfield was a first-team All-American and won Big Ten defensive back of the year honors, beating out Ohio State cornerback Jeff Okudah, a projected top-10 pick.
ESPN's Adam Rittenberg contributed to this report.