McCrimmon began his junior career at the age of 15 with the Prince Albert Raiders of the Saskatchewan Junior Hockey League (SJHL). He played two seasons with the team, scoring 23 goals and 84 points. In his second season, 1975–76, he was named the SJHL's defenceman of the year. For the 1976–77 season, he moved up to the Brandon Wheat Kings of the Western Canada Hockey League (WCHL). He scored 84 points in 72 games in his first WCHL season and added 13 points in 15 playoff games as the Wheat Kings reached the league championship series, only to lose to the New Westminster Bruins. McCrimmon scored 97 points in 1977–78 and 98 in 1978–79. He was named the defenceman of the year in 1978 and was named to the league all-star team in both seasons. He also joined the Canadian junior team at the World Junior Championship in each season. He recorded two assists in six games to help Canada win a bronze medal at the 1978 tournament and had three points in five games in 1979 though Canada failed to medal.