A co-cathedral is a cathedral church which shares the function of being a bishop's seat, or cathedra, with another cathedral, often in another city (usually a former see, anchor city of the metropolitan area, and/or the civil capital). Instances of this occurred in England before the Protestant Reformation in the dioceses of 'Bath and Wells,' and of 'Coventry and Lichfield.' These two dioceses were each named for both cities that served as bishop's seats.
As per March 2014, the Catholic church had 303 Co-cathedrals, mainly in Europe (138 in Italy alone).
Many are former cathedrals, but even if still in use, those often are not granted co-cathedral status.
Often the (arch)diocese with one or more co-cathedral(s) also has a multiple ("hyphenated") name, reflecting this/these, but some have a co-cathedral not mentioned in the title while other former see titles may also be preserved without having a co-cathedral. Sometimes the first-named city does not have the main cathedral (actual see), but boasts another distinction, such as being a national capital or having an august ecclesiastical past.
This section is incomplete. This is because not all co-cathedrals are listed in Europe, notably in Italy. (April 2017)
In Albania, the Roman Catholic Archdiocese of Tirana-Durrës has a co-cathedral in Durrës, Saint Lucia co-cathedral.
Cathedral of St. Michael and St. Gudula in Brussels
In Belgium, the cathedral of the primatial Roman Catholic Archdiocese of Mechelen-Brussels is the Metropolitan St. Rumbold's Cathedral in Mechelen (Malines), the archiepiscopal seat. Its co-cathedral is the Cathedral of St. Michael and St. Gudula in Brussels, the national capital. A third, larger church in Koekelberg (also in Brussels) has the status of minor basilica, without co-cathedral rank, yet it has received papal visits including a papal beatification.
The Roman Catholic Diocese of Sofia and Plovdiv has, besides the Cathedral of St Louis in Plovdiv, a new co-cathedral of St. Joseph in Sofia.
The Metropolitan archbishop of Split-Makarska has, in Split (Dalmatia), the co-cathedral of Saint Peter the Apostle Konkatedrala sv. Petar Apostola, besides his episcopal see, Katedrala Sv. Dujma.
The Roman Catholic Diocese of Ostrava-Opava has a co-cathedral of Our Lady of the Assumption Co-Cathedral in Ostravian-Opavian diocese in Opava besides the Ostrava Savior cathedral.
The primatial Metropolitan see of the Roman Catholic Archdiocese of Esztergom-Budapest has its primary cathedral in the old archiepiscopal seat, the Cathedral Basilica of Esztergom, and a co-cathedral basilica in the national state capital Budapest.
- The Diocese of Adria-Rovigo has a Concattedrale di S. Stefano Papa e Martire Concattedrale dedicated to Martyr Pope Stephen I in Rovigo, which never was a diocese, besides Adria's own Cattedrale di SS. Pietro e Paolo dedicated to Saints Peter and Paul
- The Roman Catholic Diocese of Alghero-Bosa (on Sardinia) has a Marian Co-Cathedral Concattedrale di Beata Vergine Immaculata Concattedrale di Beata Vergine Immaculata, in Bosa besides its cathedral episcopal see, the Marian Cattedrale di Beata Maria Vergine Immaculata Concezione, in Alghero
- The Diocese of Diocese of Amalfi-Cava de' Tirreni has a Marian Co-Cathedral of the Visitation of Mary in Cava de' Tirreni, besides the cathedral of Apostle Andrew in Amalfi.
- The Diocese of Avezzano has its cathedral in that city and a co-cathedral in its former see Pescina
- The Roman Catholic Archdiocese of Campobasso-Boiano has a
- The Roman Catholic Diocese of Lucera-Troia has its cathedral in Lucera, present see; Troia's former cathedral serves as co-cathedral
- The Diocese of Melfi-Rapolla-Venosa has a Cathedral, a Marian Minor Basilica: Basilica Cattedrale di S. Maria Assunta, at Melfi, and two Co-cathedrals: Concattedrale di S. Andrea in Venosa, and Concattedrale di S. Michele Arcangelo, in Rapolla
- The Roman Catholic Diocese of Molfetta-Ruvo-Giovinazzo-Terlizzi has a cathedral in Molfetta and three co-cathedral: in Ruvo, Giovinazzo and Terlizzi
- The Roman Catholic Diocese of Pitigliano-Sovana-Orbetello has a cathedral of Peter&Paul in Pitigliano and a co-cathdral of the Assumptio in Orbetello
- The Archdiocese of Rossano-Cariati has a Marian Cathedral di Maria SS. Achiropita at Rossano and a Co-Cathedral of the Archangel Michael in Cariati
- The Archdiocese of Sant'Angelo dei Lombardi-Conza-Nusco-Bisaccia has its cathedral in Sant'Angelo dei Lombardi and three co-cathedrals in absorbed former bishoprics : Conza di Campania, Nusco and Bisaccia
- The Diocese of Teggiano-Policastro has a Co-cathedral of the Assumption in Policastro Bussentino and a Marian cathedral of S. Maria Maggiore e S. Michele Arcangelo, in Teggiano
- The Diocese of Termoli-Larino has its cathedral in Termoli and a co-cathedral in Larino
The metropolitan cathedral of the Roman Catholic Archdiocese of Malta is St. Paul's Cathedral in the former capital Mdina. Since the 1820s, the former Conventual Church of St. John in Valletta has been known as St. John's Co-Cathedral.
- The Diocese of Calahorra y La Calzada-Logroño has a Co-cathedral of St Mary in Logrono besides its cathedral see in Calahora
- Co-cathedral of Santa María de la Fuente la Mayor in Guadalajara, Spain.
- The Diocese of Osma-Soria has a Co-cathedral of St-Peter in Soria besides its cathedral in Osma
- Latin Diocese of Kyiv-Zhytomyr has a Co-cathedral of the Merciful Father, in Zaporizhia, besides its Kiev cathedral see of Holy Wisdom
- Latin diocese of Kharkiv-Zaporizhia has a Co-cathedral of St. Sophia, in Zhytomyr, besides the Cathedral of the Blessed Virgin Mary in Kharkiv
- The Roman Catholic Diocese of Odessa-Simferopol plans a co-cathedral in Simferopol, on Criea, besides its Odessa cathedral, buts suspended building plans after the Russian annexation
The Latin Apostolic Vicariate of Alexandria had a St. Catherine cathedral in Alexandria and two co-cathedrals: the former cathedrals of the merged-in apostolic vicariates of Heliopolis of Egypt (Our Lady, in that Cairo suburb) and of Port Said (Our Lady and St. Michael in that Sinai Canal port).
The Diocese of Keta-Akatsi has its co-cathedral at first-named Keta, the cathedral is in second-named Akatsi.
Catholic Central America and Antilles
- Our Lady of Guadalupe Co-Cathedral in Belmopan is the diocesan co-cathedral of Belize City-Belmopan since the national capital was shifted to Belmopan, which was added to the bishopric's title, but the see and Holy Redeemer Cathedral remained in former capital Belize City.
- The Metropolitan Archdiocese of Los Altos Quetzaltenango-Totonicapán has a Concatedral San Miguel Arcángel, in Totonicapán, besides the episcopal see Catedral del Espíritu Santo, in Quetzaltenango.
- The diocese of Zacapa (y Santo Cristo de Esquipulas) has catedral San Pedro (dedicated to saint Peter), in Zacapa and a virtual Co-cathedral, Basílica del Cristo Negro de Esquipulas, which is officially still the cathedral of the (absorbed) Territorial Prelature of Santo Cristo de Esquipulas.
- The Metropolitan Archdiocese of Fort-de-France-Saint-Pierre has a co-cathedral Co-cathédrale Notre Dame de l'Assomption, in Saint-Pierre, besides the cathedral Cathédrale Saint-Louis, in Fort-de-France.
Catholic South America
Papua New Guinea
- The Archdiocese of Rabaul has besides its episcopal see -a cathedral in Vunapope- St Francis Xavier's Co-Cathedral, in the national capital Rabaul.
Church of England
Prior to the Protestant Reformation, the dioceses of 'Bath and Wells' and 'Coventry and Lichfield' were the only co-cathedrals in England.
Only one diocese of the Church of England has co-cathedrals; in the Anglican Diocese of Leeds there are three co-cathedrals Ripon, Bradford and Wakefield. The Diocese of Leeds was formed in 2014 by the merger of the former Anglican dioceses of Bradford, Ripon, and Wakefield, with all three former diocesan cathedrals given co-equal stats in the new diocese.
In the case of York the collegiate churches of Beverley, Ripon and Southwell were almost in the same position, but although the archbishop had a stall in each, he had no diocesan cathedra in them. The chapters were not united with that of the metropolitan church in the direct government of the diocese, or the election of the archbishop, nor had they those other rights which were held to denote the cathedral character of a church.
Scottish Episcopal Church
The Diocese of Argyll and The Isles of the Scottish Episcopal Church has two co-cathedrals: St John's Cathedral, Oban and Cathedral of The Isles, Millport, Cumbrae. It is the only diocese to have more than one cathedral.
Basilica of the National Shrine of the Assumption of the Blessed Virgin Mary in Baltimore
Co-Cathedral of the Sacred Heart in Houston
In the United States, there are several instances in which a Roman Catholic diocese maintains two Episcopal See cities, each with its own cathedral or co-cathedral. Examples include the Cathedral of Saint Paul and the Basilica of Saint Mary in the Archdiocese of Saint Paul and Minneapolis (Minnesota). Another is St. Mary's Cathedral Basilica and the Co-Cathedral of the Sacred Heart in the Archdiocese of Galveston-Houston (Texas).
Other instances include the Diocese of Altoona-Johnstown (Pennsylvania), the Diocese of Fort Wayne-South Bend (Indiana), the Diocese of Great Falls-Billings (Montana), the Diocese of Houma-Thibodaux (Louisiana), the Diocese of Kansas City-Saint Joseph (Missouri), the Diocese of Pensacola-Tallahassee (Florida), the Diocese of Springfield-Cape Girardeau (Missouri), and the Diocese of Wheeling-Charleston (West Virginia).
There are also five instances in the United States in which a cathedral and its co-cathedral are in the same city. This usually occurs when a historically important cathedral becomes too small to serve a growing population, and a larger co-cathedral is constructed to accommodate larger services. Examples include:
Examples in Canada are:
In the Episcopal Church, both the Diocese of Iowa and the Diocese of Minnesota each have two cathedrals, both located in different cities; however, they are not styled "co-cathedrals."