The 1917-18 Thunder Bay Senior Playoffs were won by the Port Arthur Columbus Club who had a 6-1-0 won-lost-tied record. They challenged for the Allan Cup. The series was scheduled to be a two game total goal series. The first game was played on March 6, 1918. They lost twenty to two. They condeded the series after the first game.
There is no further information on the district playoffs itself.