Johnson graduated from Aynor (S.C.) High School in 2008. In his senior year, he earned first-team all-state honors as selected by the Associated Press. Johnson played in the 71st-annual Shrine Bowl of the Carolinas. Rivals.com ranked him as a three star prospect, the 13th-best offensive center in the nation and the 17th-best player in the state of South Carolina. Johnson ultimately chose South Carolina over offers from Vanderbilt, Duke, Wake Forest, East Carolina, Kentucky, Maryland and N.C. State.