The Diocese of Timmins was originally established on December 31st, 1915 as the Diocese of Haileybury. After losing several parts of its territory to the Prefecture Apostolic of Northern Ontario, the Dioceses of Amos and the Vicariate Apostolic of James Bay, on December 10, 1938, the name was changed to the Diocese of Timmins. The Diocese comprises the south eastern part of the District of Cochrane, and the entire District of Timiskaming.