2009-10: Cooper skated in 55 games for the Fargo Force in his first USHL season. He scored 3 goals with 10 assists and was plus-seven with 69 penalty minutes. Fargo reached the Clark Cup Finals after finishing second in the Western Conference and in 13 playoff games Cooper had 4 assists and was plus-five with 22 penalty minutes.
2010-11: Cooper was the leading scorer among Force defensemen in his second season with Fargo and played for the USA in the 2011 U19 World Junior A Challenge. He scored 11 goals with 22 assists and was plus-15 with 132 penalty minutes in 51 games. Fargo slipped to fifth in the West and lost in the second round of the playoffs. In five playoff games Cooper scored 2 goals and was plus-four with 18 penalty minutes. Cooper was named to the USHL All Star Game. In four games at the Junior A Challenge he scored 1 goal with 1 assist and 10 penalty minutes. He committed to playing college hockey at Nebraska-Omaha in 2012-13.
2011-12: Cooper skated in 55 games for Fargo in his final USHL season and again competed in the U19 World Junior A Challenge. He scored 6 goals with 18 assists and was a career-best plus-16 with 92 penalty minutes. The Force again reached the second round of the playoffs and in six playoff games Cooper scored 1 goal with 2 assists and was an even plus/minus with 8 penalty minutes. In five games at the Junior A Challenge he had 3 assists and 8 penalty minutes. He was invited to the NHL Draft Combine and ranked 68th amongst North American skaters in Central Scouting's final rankings prior to the 2012 NHL Draft.
Cooper is sort of a “kitchen sink”-type of defender only lacking decent size. His defensive game is sound, and he isn't afraid to take the body despite his modest size. On the offensive side of the ledger, he is a good skater with good passing skills and a good shot, so he is able to contribute at both ends of the ice. If Cooper can add some bulk without affecting his overall game, he could become second- or third-pairing defenseman.