The Diocese of Ontario is a diocese of the Ecclesiastical Province of Ontario of the Anglican Church of Canada, itself a province of the Anglican Communion. Its See city is Kingston, Ontario, and its Cathedral is St. George's, Kingston. The diocese is not coterminous with the Canadian civil Province of Ontario, but rather encompasses approximately 17,700 square kilometres of it, comprising the Counties of Prince Edward, Hastings, Lennox and Addington, Frontenac, and Leeds and Grenville. Apart from Kingston, other major centres included in the diocese are Belleville, Brockville, and Trenton. The diocese ministers to approximately 13,000 Anglicans in forty-two parishes.
The diocese was founded in 1862, when it was divided from the Diocese of Toronto. The Diocese of Ontario was incorporated by “An Act Respecting The Incorporated Synod of Ontario”. Until 1896 it included the present-day Diocese of Ottawa. Its first bishop, John Travers Lewis, a Church of Ireland cleric, was the first bishop consecrated in Canada rather than England.