| Jurisdiction: | Diocese |
| Saint-Jean–Longueuil | |
| Latin: | Dioecesis Sancti Ioannis–Longoliensis |
| Local: | French: Diocèse de Saint-Jean Longueuil |
| Coat: | Diocese_of_Saint-Jean-Longueuil.jpg |
| Coat Size: | 200px |
| Country: | Canada |
| Territory: | Montérégie |
| Province: | Archdiocese of Montréal |
| Area Km2: | 2,078 |
| Population: | 762,240[1] |
| Catholics: | 634,425 |
| Catholics Percent: | 83.2 |
| Parishes: | 45 |
| Denomination: | Catholic Church |
| Rite: | Roman Rite |
| Established: | June 9, 1933 |
| Cathedral: | Cathedral of Saint-Jean-l'Évangéliste |
| Cocathedral: | Co-Cathedral of Saint-Antoine-de-Padoue |
| Patron: | John the Evangelist |
| Priests: | 60 |
| Bishop: | Claude Hamelin |
| Metro Archbishop: | Christian Lépine |
| Emeritus Bishops: | Lionel Gendron, P.S.S. |
| Website: | dsjl.org |
The Roman Catholic Diocese of Saint-Jean–Longueuil (la|Dioecesis Sancti Ioannis–Longoliensis) is a suffragan of the Metropolitan Archdiocese of Montréal in (mostly francophone) Québec, southeastern Canada.
Its cathedral episcopal see is the Cathédrale Saint-Jean-l’Évangéliste dedicated to John the Evangelist, in Saint-Jean-sur-Richelieu.
It has a Co-Cathedral: Cocathédrale Saint-Antoine-de-Padoue, dedicated to Saint Anthony of Padua, in Longueuil, Québec, and a Minor basilica: Basilique Sainte-Anne-de-Varennes, in Varennes, Québec.
As per 2015, it pastorally served 634,425 Catholics (83.2% of 762,240 total) on in 45 parishes and 1 mission with 89 priests (60 diocesan, 29 religious), 4 deacons, 350 lay religious (99 brothers, 251 sisters) and 4 seminarians.
(all Roman Rite native Canadians)