Johnson is a 2008 graduate of Keene State and while at KSC, he helped lead the lacrosse program to the top of Division III. During his career at Keene, Johnson was named as the 2005 Little East Conference (LEC) Rookie of the Year, a four-time First Team All-Conference selection (2005-2008) and was a three-time LEC Defensive Player of the Year (2006-2008).

In addition, Johnson was honored as the ECAC Goalie of the Year, the NEILSA First Team, a USILA Division III Honorable Mention All-American and the 2007-2008 Keene State College Male Athlete of the Year. Johnson led all of NCAA Division III in save percentage at 71.3 percent, en route to an NCAA Tournament appearance for the Owls. He also took part in the USILA Senior North/South All-Star game, as well as the NEILA Senior East/West All-Star game.

While playing high school lacrosse at Pinkerton Academy, Johnson won two NHIAA State Championships, was named as a First Team All-State selection three times and was a U.S. Lacrosse All-American in 2004. During his senior season, he was honored by being selected to the Warrior National HS North/South Game.