2009-10: Eamon McAdam played for Team Comcast U16 in suburban Philadelphia and was the top goaltender in the 2010 Liberty Bell Games. In 23 games he had a 2.47 goals against and .920 save percentage. He was selected by the London Knights in the fourth round (75th overall) of the 2010 OHL Priority Draft.
2010-11: McAdam made his USHL debut, appearing in four games for the Waterloo Black Hawks, and played nine games for the Austin Bruins in the NAHL. He was 2-2 with Waterloo and had a 3.48 goals against and .888 save percentage. One of five goalies to see action for the Bruins behind starter Keegan Asmundson, McAdam was 2-4-2 with a 3.32 goals against and .904 save percentage. He committed to playing college hockey at Penn State in 2013-14.
2011-12: Part of a crowded goaltending picture for Waterloo in his first USHL season, McAdam appeared in a team-high 23 games during the regular season. He finished the year 11-7 and had a 3.50 goals against and .882 save percentage. Waterloo finished third in the West Division and reached the playoff finals against Green Bay. Nineteen-year-old Stephon Williams started all 15 playoff games for Waterloo.
2012-13: McAdam returned to Waterloo for his second full season, splitting the goaltending duties with fellow 2013 NHL Draft prospect Cal Petersen. In 31 games he was 17-9-3 with two shutouts and had a 3.45 goals against and .896 save percentage. He appeared in two games in the playoff series with Fargo, making one start, and was 0-1 with a 3.22 goals against and .922 save percentage. The Black Hawks represented the USHL in the pre-season 2013 World Junior Club Cup in Omsk, reaching the semifinals, and in four games McAdam was 3-1 with a 2.17 goals against and .915 save percentage. He represented the USA in the 2012 World Junior A Challenge and was 4-0 with a 2.18 goals against and .927 save percentage for the gold medal-winning squad. McAdam was ranked sixth amongst North American goaltenders in Central Scouting's final rankings prior to the 2013 NHL Draft.