Cook left Providence to become head coach of the Cleveland Barons in 1943–44. The Barons won their division six times in Cook's first nine seasons as coach. They reached the Calder Cup Final on six occasions in that time and won three championships: in 1944–45, 1947–48 and 1950–51. He was considered a favourite to become head coach of the Boston Bruins in 1950, but never left Cleveland. In 1952–53, Cook coached the Barons to both the regular season championship and the Calder Cup as the Barons defeated the Pittsburgh Hornets by a 1–0 score in overtime of the seventh, and deciding, game of the series. Cook coached the Barons to a repeat championship in 1953–54, his seventh Calder Cup victory. With a record of 26–31–7, 1955–56 season was the first in 13 seasons with the Barons that Cook coached the team to a losing record. Though the team reached the league championship series, the Barons opted to relieve Cook of his position as coach.