High school and college
Born in Washington, D.C., Johnson attended Colonial Beach High School in Westmoreland County, Virginia, where he averaged 22.2 points and 12.5 rebounds in his final season. He was then part of Laurinburg Institute's prep school national championship team under coach Chris Chaney in 2005. He averaged 8.6 points, 3.9 rebounds and 2.7 blocks per game as a senior and shot 42 percent from three-point range.
Johnson played college basketball for the LSU Tigers from 2005 to 2009. In 85 games, he made 59 starts and averaged 7.2 points, 5.2 rebounds and 2.0 blocks in 20.4 minutes per game. With 176 blocks, he finished his four-year career as the second all-time leader in blocked shots at LSU behind Shaquille O'Neal (412).