2009-10: Joonas Korpisalo skated for Jokerit's U16 team in Finland's top division after playing his earlier youth hockey with the Karhu-Kissat club. In 22 games he was 13-4 with one shutout and had a 2.28 goals against and .930 save percentage. Jokerit won the U16 championship and in 13 playoff games Karpisalo was 9-4 with 1 shutout and had a 2.58 goals against and .937 save percentage.
2010-11: Korpisalo played with Jokerit's U18 team in his second season with the club and skated in two games for Finland's U17 team in international play. Korpisalo appeared in 23 games and in 15 starts was 13-2 with a 2.55 save percentage and .924 goals against. Jokerit reached the U18 bronze medal game and in nine playoff games Korpisalo was 5-3 with 2.87 goals against and .916 save percentage. In two games with Finland's U17 team he had a 1.46 goals against and .914 save percentage.
2011-12: Korpisalo was the starting goalie for Jokerit's U20 team and handled the bulk of the goaltending for Finland at the 2012 U18 World Junior Championship. Korpisalo received the Jorma Valtonen Award as the best goalie in Finnish junior hockey. In 45 games he was 28-11 with 4 shutouts and had a 2.04 goals against and .920 save percentage. Jokerit finished first in the regular season and reached the playoff championship series. Edmonton prospect Frans Tuohimaa handled the bulk of the goaltending in the playoffs as Jokerit finished second. In four starts Korpisalo was 3-1 with 1 shutout and had a1.77 goals against and .927 save percentage. Korpisalo was 3-3 with one shutout and had a 3.02 goals against and .902 save percentage in seven games for fourth-place Finland at the U18 WJC. He was invited to the NHL Draft Combine and ranked third amongst European goaltenders in Central Scouting's final rankings prior to the 2012 NHL Draft.
Korpisalo is extremely athletic and relies heavily on his strong legs to move smoothly on the ice. He has great speed pipe to pipe and is not afraid to move out of his crease. The only problem with his aggressive nature is that he has trouble differentiating between when to be aggressive and when to stay at home, but that should come through maturity and experience.
Instead of staying in Finland, Korpisalo entered the WHL Priority draft and was picked fifth overall by the Prince George Cougars. The Cougars have every intention to give him playing time early and should have at least two seasons to adjust to the North American style of play.