 | 1816 | 1817 | 1818 |  |
Date | Country | Change |
| 1817 |  Italy | Diocese of Bertinoro was restored (from Metropolitan Archdiocese of Ravenna) |
| 1817 |  Lebanon | Diocese of Beirut (Syriac Rite) was established (became suffragan of Antioch) |
| 1817 |  Syria,  Iraq | Mission sui juris of Syria and Cilicia was promoted as Apostolic Prefecture of Syria and Cilicia |
| 1817 | Syria | Apostolic Vicariate of Aleppo was renamed as Apostolic Vicariate of Syria, Egypt, Arabia and Cyprus |
| 1817.02.08 | Italy | Diocese of Treia was restored (from Archdiocese of Camerino) |
| 1817.03.17 | Italy | Diocese of Nicosia was established (from Metropolitan Archdiocese of Messina and Diocese of Catania and became suffragan of Messina) |
| 1817.07.03 | Italy | Diocese of Piazza Armerina was established (from Diocese of Catania and became suffragan of Monreale) |
| 1817.07.04 |  Canada | Apostolic Vicariate of Nova Scotia was established (from Diocese of Québec) |
| 1817.07.10 |  France | Diocese of Chambéry was promoted as Metropolitan Archdiocese of Chambéry |
| 1817.07.17 | Italy | Diocese of Alba was restored (from Diocese of Asti and Diocese of Mondovì and became suffragan of Torino) |
| 1817.07.17 | Italy | Diocese of Alessandria was restored (from Diocese of Casale Monferrato and became suffragan of Vercelli) |
| 1817.07.17 | Italy | Diocese of Aosta was restored (from Diocese of Ivrea and became suffragan of Chambéry) |
| 1817.07.17 | Italy | Diocese of Asti lost territory to Diocese of Mondovì |
| 1817.07.17 | Italy | Diocese of Biella was restored (from Diocese of Vercelli and became suffragan of Vercelli) |
| 1817.07.17 | Italy | Diocese of Casale Monferrato lost territory to Diocese of Acqui |
| 1817.07.17 | Italy | Diocese of Cuneo was established (from Diocese of Mondovì and became suffragan of Torino) |
| 1817.07.17 | Italy | Diocese of Fossano was restored (from Diocese of Mondovì and became suffragan of Torino) |
| 1817.07.17 | Italy | Metropolitan Archdiocese of Milano (Ambrosian Rite) lost territory to Diocese of Novara and Diocese of Vigevano |
| 1817.07.17 | Italy | Diocese of Mondovì lost territory to Metropolitan Archdiocese of Torino and Diocese of Saluzzo |
| 1817.07.17 | Italy | Diocese of Novara lost territory to Diocese of Vigevano |
| 1817.07.17 | Italy | Diocese of Pavia lost territory to Diocese of Vigevano |
| 1817.07.17 | Italy | Diocese of Pinerolo was restored (from Diocese of Saluzzo and became suffragan of Torino) |
| 1817.07.17 | Italy | Diocese of Susa was restored (from Metropolitan Archdiocese of Torino and became suffragan of Torino) |
| 1817.07.17 | Italy | Diocese of Tortona was restored (from Diocese of Casale Monferrato, Diocese of Pavia and Diocese of Piacenza and became suffragan of Genova) |
| 1817.07.17 | Italy | Diocese of Vercelli was promoted as Metropolitan Archdiocese of Vercelli (with suffragan sees Alessandria, Biella and Casale Monferrato and lost territory to establish Diocese of Biella) |
| 1817.07.27 | France | Diocese of Moulins was established (from Diocese of Autun) |
| 1817.10.29 | Italy | Diocese of Alba lost territory to Diocese of Mondovì |
| 1817.11.22 |  Suriname | Apostolic Prefecture of Dutch Guyana–Suriname was established (from Mission sui juris of Batavia) |
| 1817.11.23 | Italy | Diocese of Bobbio was restored (from Diocese of Casale Monferrato and became suffragan of Genova) |
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