The Apostolic Prefecture of Placentia was a short-lived (1870–91) Catholic pre-diocesan jurisdiction in Newfoundland.

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It was named after its see, Placentia, an alamagated town on the Avalon Peninsula, Newfoundland and Labrador.

• Established on 16 September 1870 as Apostolic Prefecture of Placentia / Placentia (Latin), on territories split off from the then Archdiocese of St. John's (which it was held in personal union with) and Diocese of Harbour Grace.
• Suppressed in 1891, its territory being reassigned to the above St. John's, Newfoundland, which it in effect merged (back) into.

Its only episcopal leader was :

• Thomas James (born Ireland) (1870.05.09 – see suppressed 1891), also Bishop of St. John's, Newfoundland (1870.05.08 – death 1893.12.04).