 | 1839 | 1840 | 1841 |  |
Date | Country | Change |
| 1840 |  Albania | Archdiocese of Durrës (Albanese Rite) was suppressed |
| 1840 |  Belarus | Titular Episcopal See of Pinsk–Turaŭ (Ukrainian Rite) was suppressed |
| 1840 |  England | Diocese of Eastern District was established (from Apostolic Vicariate of Midland District) |
| 1840 | England,  Isle of Man | Apostolic Vicariate of Lancashire District was established (from Apostolic Vicariate of Northern District) |
| 1840 | England | Apostolic Vicariate of Wales District was established (from Apostolic Vicariate of Western District) |
| 1840 |  Lebanon | Diocese of Batroun–Jbeil (Maronite Rite) lost territory to Archdiocese of Tripoli |
| 1840 |  Netherlands | Apostolic Vicariate of Limburg was restored (from Metropolitan Archdiocese of Köln and Diocese of Liège) |
| 1840 |  Palestine | Titular Episcopal See of Bethlehem was restored (from former Diocese of Bethléem à Clamecy) |
| 1840 |  United Arab Emirates,  Oman,  Yemen | Apostolic Prefecture of Jedda was established (from Apostolic Vicariate of Egypt and Arabia) |
| 1840.04.27 |  USA | Diocese of California was established (from Diocese of Sonora and became suffragan of México) |
| 1840.05.11 | England | Apostolic Vicariate of Yorkshire District was established (from Apostolic Vicariate of Northern District) |
| 1840.05.21 |  Chile | Diocese of Santiago was promoted as Metropolitan Archdiocese of Santiago (with suffragan see Concepción) |
| 1840.06.02 |  Luxembourg | Apostolic Vicariate of Luxembourg was established (from Diocese of Liège and Diocese of Namur) |
| 1840.07.01 | Chile | Diocese of La Serena was established (from Metropolitan Archdiocese of Santiago and became suffragan of Santiago) |
| 1840.07.01 | Chile | Diocese of San Carlos de Ancud was established (from Diocese of Concepción and became suffragan of Santiago) |
| 1840.07.03 | England | Apostolic Vicariate of Midland District was renamed as Apostolic Vicariate of Central District |
| 1840.08.20 |  China | Apostolic Vicariate of Liaotung 遼東 was renamed as Apostolic Vicariate of Liaotung and Manchuria 遼東滿州 (lost territory to establish Apostolic Vicariate of Mongolia 蒙古) |
| 1840.08.20 | China | Apostolic Vicariate of Mongolia 蒙古 was established (from Apostolic Vicariate of Liaotung 遼東) |
| 1840.08.28 | China | Apostolic Vicariate of Yunnan 雲南 was restored (from Apostolic Vicariate of Szechwan 四川) |
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