Irish Genealogy and Geography - Diocese Map
The Dioceses of Ireland
Territorial History

Irish Diocesan Boundaries in the Middle Ages
Also see 19th century Diocesan Boundaries

From the time of St. Patrick in the 5th century to the Synod of Rathbreasail in Ireland in 1111 AD monastic settlements, rather than dioceses, characterised the organisational structure of the Irish Church. Church reformation beginning in the mid-11th century throughout western Christendom, known as the Georgian movement, reached Ireland in the early 12th century. The Synod of Cashel in 1101 passed decrees forbidding lay abbots, divorce, incest and clerical marriage. The Synod of Raith Bressail in 1111 introduced a diocesan system with the two ecclesiastical provinces of Armagh and Cashel. This was modifed at the Synod of Kells-Mellifont in 1152, when Tuam and Dublin were elevated to archbishoprics estabishing a diocesan system throughout Ireland. At the same time the primacy of the Irish Church was moved from Canterbury to Armagh.

Diocesan boundaries were largely based on the territorial boundaries of Irish dynasties and were centered around well known monastic sites, many of which were first established in the 6th and 7th centuries. This page partially explores the relationship of early Irish dynastic territories and the establishment of diocesan boundaries in the 12th century. Although individual dioceses have merged or changed names since that time, diocesan boundaries have changed little in the convening centuries and offer a unique glimpse into the Ireland's Gaelic past.


Diocese of Achonry

Approximately co-extensive with the ancient territory of Luigne (Leyney in Sligo) and Gailenga (Gallen in Mayo), the diocese of Achonry was not among the five dioceses assigned to the western province of Connacht by the Synod of Rathbreasil in 1111; i.e. Tuam, Clonfert, Cong, Killala and Ardcarne. Tradition alone claims Achonry to have been an ancient bishopric. It was formally erected by the Synod of Kells in 1152. The monastery at Achonry in Co. Sligo was founded by Finian of Clonard at some date in the sixth century.
Parish Map of Achonry

Diocese of Ardagh (and Clonmacnois) - Achadh-Chonnaire

The diocese originally comprised the country of the Eastern Conmaicne, and was formerly known as the diocese of Conmaicne (ref: Irish Annals). It consisted of the territory of the O'Ferals (O'Farrell) and the O'Quinns in the county Longford, called Annally, and the territory of Muintir Eolais (aka Conmaicne Rein), of MacRannal (O'Reynolds) in southern Co. Leitrim. The former Diocese of Clonmacnoise was said to be united to that of Ardagh in the 1750s. The modern Diocese of Ardagh includes nearly all of Longford, the greater part of Leitrim, and portions of King's County, Westmeath, Roscommon, and Sligo.
Parish Map of Ardagh

Diocese of Ardfert (now part of Kerry)

The Diocese of Kerry, originally the ancient Sees of Ardfert and Aghadoe, extends over the whole County of Kerry and a portion of that of Cork. Before the Synod of Rathbreasail (1111), the ancient Sees of Ardfert and Aghadoe had already been united, and the See was located at Rathass near Tralee. In 1111 the Diocese of Ráith Maighe Deiscirt was established which was co-extensive with with the area of Iarmhumha. At the Synod of Kells in 1152, however, the corresponding diocese was called Ardfert, a title that was retained until modern times, when the diocese became known as Kerry.
The ancient bishopric of Ardfert comprehended the northern part of County Kerry, and anciently called Ciaragi. In turn, the ancient See of Aghadoe comprehended the southern part of County Kerry and probably a small part of western Co. Cork. The tribal territories of the Ciarraige, Corcu Duibne, Uí Cairpri Luachra and Éoganacht Locha Lein were noted in Ardfert & Aghdoe at the time the diocesan boundaries were established.
Parish Map of the Diocese of Kerry

Diocese of Armagh - Ard Macha

The Archdiocese of Armagh at present comprises almost the whole of the counties Armagh and Louth, a great part of Tyrone, and portions of Derry and of Meath. The boundaries drawn in the 12th century likely included that of the ancient territory of Oirghialla (Oriel) and in the next century that of the Conaille Muirtheimhne (of Louth). Following the 12th century the ruling Irish families in the north of the diocese were the Uí hAnluain (O'Hanlons) and their powerful sponsors the Uí Neill, while the southern portion of the diocese was held by the Anglo-Normans. In all ancient Synods and visitations the clergy of the English and Irish parts were congregated separately, the clergy of southern part assembling for visitation at Drogheda, and those of the northern at Armagh. In 1247, Archbishop Rayner separated the county of Louth from the diocese of Clogher, and annexed it to Armagh.
In 1152, Cardinal Paparo placed the following Sees under the jurisdiction of the archbishop of Armagh: Connor, Dumdaleghlas (now Down), Lugud, Cluainaird (or Clonard), Connanas, Ardachad (now Ardagh), Rathboth (now Raphoe), Rathlurig (or Rathlure), Damliag, and Darrick (now Derry).
Parish Map of the Diocese of Armagh

Diocese of Cashel - Caiseal

At the Synod of Kells 1152, Cardinal Paparo gave a pallium to Donat O'Lonergan of Cashel, and since then his successors have ruled the ecclesiastical province of Munster (Cashel), probably co-extensive with the ancient territory of the Eoghanacht Caiseal in Co. Tipperary. The modern Catholic Ecclesiastical Province of Cashel comprises the Archdiocese of Cashel with the Diocese of Emly and eight suffragan Sees: Cloyne, Cork, Kerry, Killaloe, Limerick, Ross, Waterford & Lismore, and Kilfenora. The Bishop of Galway is Apostolic Administrator of Kilfenora.
In the late 12th century the following bishoprics are noted under the metropolitan jurisdiction of the archbishopric of Cashel: Limerick, Killaloe, Fennabore (Kilfenora), Waterford, Ardmore, Limore, Cloyne, Cork, Ross, Ardfert, and Emly.
Map of the Archdiocese of Cashel and Emly

Diocese of Clogher - Clogherensis

The modern Diocese of Clogher comprises the County Monaghan, almost the whole of Fermanagh, the southern portion of Tyrone, and parts of Donegal, Louth, and Cavan. It takes its name from Clogher, the seat of the Prince of Oriel, with whose territory the old Diocese of Clogher was, practically speaking, coextensive. So late as the 12th century, Edan O'Killedy, bishop of the See, subscribed his name as Bishop of Uriel (Oriel , or more anciently Oirghialla). The ancient See of Clones was at a remote period annexed to it, as also were those of Ardsrath and Louth.
It was under Bishop David O'Brogan that large portions of Tyrone were cut off from Clogher and given to Ardstraw (aka Rathlure, now united with Derry), while the greater part of the present County Louth, including Dundalk, Drogheda, and Ardee, was taken over by Armagh. It was about 1266 that the bishopric of Ardstraw was taken possession of by the Bishop of Derry, and Louth by the Archbishop of Armagh.
Outline map of Clogher

Diocese of Clonfert - Clonfertensis

Clonfert ,or Cluain Fearta Breanainn, founded by St. Brennan in the 6th century was roughly co-extensive with that part of the ancient territory of Uí Maine (or O'Kelly country) later held by the O'Maddens (of Sil Anmchada). The O'Kellys and O'Maddens were ruling families in Uí Maine during the 12th century when the diocesan boundary was established. In Gaelic Clonfert is referred to as Cluain-fearta Brenainn.
Outline map of Clonfert

Diocese of Cloyne - Cluain-uania

The Diocese of Cloyne comprises the northern half of County Cork. The ancient territories of the Muscraige, Éoganacht Glendamnacht and Úi Liatháin are noted here. In 1152 (Synod of Kells) Cloyne was made one of Cashel's twelve suffragan Sees (of a total 38 established in all of Ireland at that Synod). In 1431 the two Sees of Cloyne and Cork were united until 1638, when they were again separated and the Sees of Cork and Ross were united. In 1653, the See of Cloyne was again united to the Sees of Cork and Ross until in 1678 Cloyne was again separated. In 1835 the See of Cloyne was once more joined to that of Cork and Ross. Cloyne is one of the eleven dioceses that constitute the province of Cashel.
Map of Cloyne

Diocese of Connor - Connorensis

Oengus Mac Nisse (or St. Macnise) became the first bishop of Connor in the 6th century. A tribe named the Coindiri once held the land now covered by the diocese of Connor. Coindire, pronounced locally Conyer, had its boundaries fixed by Synod of Rathbreasail, which extended from Benn Foibne to Torbuirg, from Port Murbuilg to Ollarba, and Cuan Snámha hAigne, and from Glenn Righe to Colba Gearmain.
Connor appears anciently to have been called Dailnariagh, from its cathedral being in the territory of Dalradia, i.e. the Dál n-Araidhe dynasty centered in southern Co. Antrim. An O'Lynch sept were lords in Dál n-Araidhe in the 12th century when the boundaries of the diocese were likely laid. The northern and central sections of the diocese were said to anciently hold the territories of Dal Riada and Dal Fiatach.
In 1442 the bishoprics of Down and Connor were united, and it is still recognized as one of the 10 dioceses of the Ecclesiatical province of Armagh, the others being Armagh, Clogher, Meath, Down, [Connor], Derry, Raphoe, Kilmore, Dromore, and Ardagh.
Outline map of Down and Connor

Diocese of Cork - Corcagiensis

Formed in the Synod of Rathbreasail (1111), the boundaries of the Diocese of Cork appear to roughly coincide with the lands of the Ui Eachach Mumhan and Éoganacht Raithlind. The eastern and western limits were respectively Cork and Mizzen Head, and there are arguments to show that the northern and southern were the Avonmore (Blackwater) and the ocean. After the twelfth century part of the territory between the Lee and Blackwater to the north was detached in favour of the neighbouring Diocese of Cloyne; the land of the O'Driscolls had been already erected into the Diocese of Ross. In 1430, at the instance of the Bishop of Cloyne, the two Dioceses of Cork and Cloyne were united, and remained thus for three hundred years, until 1747. Today Cork is approximately bounded on the north by the city and suburbs, and the River Lee as far as Gougane Barra, on the east by Cork Harbour, on the south by the Diocese of Ross and the ocean, and on the west by Bantry Bay. The church and monastery founded by St. Finbarr in the late 6th century were the centre of the diocese till the sixteenth century.
Outline map of Cork

Diocese of Derry - Derriensis

The present Diocese of Derry was formed by a union of the old Sees (dioceses) of Rathlure and Ardstraw founded by St. Eugene (Eoghan), and it was fully defined about the middle of the thirteenth century. Ardstraw continued as an episcopal See until the 1150's, when it was translated to Rathlure and subsequently to Maghera, but by 1254 it was definitely removed to Derry (see Clogher). It presently includes nearly all the County Derry, part of Donegal, and a large portion of Tyrone. It was roughly co-extensive to the ancient territory of Cenel Eoghain. The diocese owes its origin to the monastic establishment founded there by St. Columba between 546 and 562.
Outline map of Derry

Diocese of Down - Dunensis

In 1137 St. Malachy (O'Morgair) accepted the bishopric of Down, which See he afterwards divided into two, reserving one to himself. It is possible that the diocese was originally included in the diocese of Connor before its separation. Its early prelates were called Bishops of Dundalethglass with its See in the modern town of Downpatrick. The MacDonlevy's were lords of Uladh, centered here at the coming of the Norman John de Courcy in 1177. The boundary of the diocese was likely related to that of the Dál Fiatach territory. In 1441 the diocese of Down was [again] united to that of Connor.
Outline map of Down and Connor

Diocese of Dromore - Drumorensis

The first bishop of Dromore in County Down was a St. Colman, who founded a monastery there probably about the year 514. "It is the will of God that you erect a monastery within the bounds of Coba plain", was the advice he received. This area was considered to be part of the ancient territory of Uladh (Ulidia) which gives its name to the province of Ulster. The territory of the Uí Eathach Cobha (Iveagh) tribe appears to be roughly co-extensive with this diocese, with the Magennis (McGuinness) sept in power at the time the diocesan boundaries were laid.
Outline map of Dromore

Diocese of Dublin - Dublinensis

At the Synod which met at Rath-Breassail in 1111, the number of Sees (dioceses) was fixed at twenty-four, Dublin excluded. Glendalough was erected into a diocese at that time and it included most of the modern diocese of Dublin, except for an area around the Danish held city of Dublin. At the Synod at Kells in 1152, Armagh, Dublin, Cashel, and Tuam, were created archiepiscopal Sees, and north County Dublin, known as Fingall, was annexed to the See of Dublin. In 1185 the See of Glendalough was to be united to that of Dublin, following the death of its current Bishop, an event which occured in 1214.
Outline map of Dublin

Diocese of Elphin - Elphinium

A monastery was founded at Ardcarn in the 6th century and at the Synod of Rathbreasail in 1111 Ardcarn was chosen as one of the five dioceses of Connacht. At the Synod of Kells in 1152, Ardcarne was amalgamated with the Sees of Elphin, Roscommon and Drumcliff to form the present diocese of Elphin. Elphin was formed from the ancient lands of the Uí Briuin Ai and Uí Aellelo, in territory held by the O'Conors and MacDermotts. among others, at that time. The present Diocese of Elphin includes nearly the whole of the county of Roscommon, with large portions of Sligo and Galway.
Parish Map of Elphin

Diocese of Emly

Emly is of great antiquity and was noticed under the name of "Imlagh" by Ptolemy in the 2nd century as one of three principal towns of Hibernia (Ireland). Since the 12th century boundaries were laid, the diocese of Emly consisted of a small portion of west Co. Tipperary, east Co. Limerick and southeast Co. Clare. The territory of the Éoganacht Áine is noted here. Since 1568 the Archbishop of Cashel has been the Administrator of the ancient Diocese of Emly.
Map of the Archdiocese of Cashel and Emly

Diocese of Ferns - Fernensis

The diocese of Ferns (or Fearna, the alder tree) was founded in 598 by St. Maodhóg (Aidan) who received a grant of land at Ferns from Brandubh, king of Uí Cinsealaigh. The boundaries of the diocese were determined by the Synod of Ráth Breasail in 1111, and likely coincides with the ancient territory of Uí Ceinnsealaigh. Edan, bishop and founder of Ferns in the 7th century, is variously spelt as Edan or Aedan, or M'-Aed-oc (Mogue).
Map of Ferns

Diocese of Kildare and Leighlin - Kildarensis et Leighlinensis

These two dioceses continued to be separate from their foundation until 1678, when the Diocese of Leighlin was given in commendam by the Holy See to the Bishop of Kildare. The Diocese of Kildare embraces the ancient territories of Uí Failge, Uí Cairpri Laigin, and Uí Faelain. The Diocese of Leighlin embraces ancient Leix (Queen's County), which connects it with Kildare and a portion of Uí Ceinnsealaigh. Kildare diocese owes its origin to the development from about the year 470 of a monastic complex at Kildare (Church of the Oak Tree) associated with the figure of St. Brigid.
Parish Map of Kildare and Leighlin

Diocese of Kilfenora

The Diocese of Kilfenora was co-extensive with the ancient territory of Corca Modhruadh (Corco Mruad). The diocese lied wholly within the county of Clare and comprehended the baronies of Burren and Corcomroe. St. Facthna founded the monastery here in the 6th century. It was anciently referred to as Fenabore and Cellumabrach. The first bishops were called Bishops of Corcomroe (Corco Mruad). In 1111 the Synod of Rathbreasil ignored Kilfenora's claim to Episcopal government. This resulted in an unusual alliance of the O'Connor and O'Loghlen clans who did not wish to see the O'Brien-dominated diocese of Killaloe taking over their own independent bishopric. This decision was overturned in 1152 at the Synod of Kells and Kilfenora was recognised as a separate entity. In 1750 the Diocese of Kilfenora was united with the larger Diocese of Kilmacduagh. By 1866 both were united to that of the Diocese of Galway (refer to the See of Enaghdune or Annaghdown).
Outline map of Kilfenora

Diocese of Killala - Alladensis

Killala comprises the north-western part of the County Mayo with the Barony of Tireragh in the County Sligo, and was approximately co-extensive with the ancient territory of the Uí Fiachrach Muiade (Moy) and Tir Amalghaid (Tirawley). The ancient successors of St. Muredach, its first bishop, were called Bishops of Tiramalgaid as well as Bishops of Uí Fiachrach Mui. In 1198, Pope Innocent III confirmed all the ancient possessions of the See.
Outline map of Killala

Diocese of Killaloe - Laonia

It comprises the greater part of County Clare, a large portion of Tipperary, and parts of King's and Queen's Counties, Limerick, and Galway. Its Irish name is Cill-da-Lua, so named from St. Lua, an abbot who lived about the end of the sixth century, and whose oratory can still be seen in Friar's Island, near the town of Killaloe. At the Synod of Rathbresail in the first quarter of the twelfth century, Killaloe assumed its present shape, which is almost coterminous with the boundaries of the ancient Kingdom of Thomond. Ancient Thomond included the territories of Dal gCais (O'Briens, et al), Aradh, Eile and Muscraige Tire in the eastern portions, and Corco Baiscinn in the southwest.
Prior to the Synod of Rath-Breassail the diocese of Killaloe did not include the old Sees of Roscrea and Inniscathy (Inniscattery). By the late 12th century the ancient bishopric of Roscrea was united to the See of Killaloe. The Diocese of Roscrea was coextensive with the territory of the O'Carrolls (Eile), along with that of the O'Kennedys. The Diocese of Inniscathy, comprised the Baronies of Moyarta, Clonderlaw, and Ibricken, in Clare; the Barony of Connello, in Limerick; and in Kerry, the ancient region of the Uí Fidgente. The parish of Seir Kieran in King's County, though in Thomond, was allowed to remain subject to the Diocese of Ossory, out of respect to the memory of St. Kieran.
Outline map of Killaloe

Diocese of Kilmacduagh - Duacensis

The Diocese of Kilmacduagh, whose name means "church of Duagh's son", was co-extensive with the territory of the Uí Fiachrach Aidhne. The See was founded by St. Colman, son of Duach, of the noble family of Uí Fiachrach. Kilmacduagh includes the whole Barony of Kiltartan, and part of Dunkellin and Loughrea in County Galway. Galway diocese includes the barony of Galway and part of Moycullen and Clare. In 1750 Kilmacduagh was united with the smaller Diocese of Kilfenora, the latter situated entirely in County Clare, and corresponding in extent with the Barony of Corcomroe. In 1866 the Bishop of Kilmacduagh being unable to discharge his duties, the Bishop of Galway was appointed Apostolic Administrator of Kilmacduagh and Kilfenora, "durante beneplacito Sanctæ Sedis". In 1883 the union of the three dioceses was made permanent by papal Bull. Since that date the bishop is "Bishop of Galway and Kilmacduagh and Apostolic Administrator of Kilfenora".
Outline map of Galway and Kilmacdough

Diocese of Kilmore - Kilmorensis

The Diocese of Kilmore includes almost all Cavan and about half of Leitrim. It also extends into Fermanagh, and has half a parish in both Meath (Kilmainham Wood) and Sligo (Ballintrillick). It is accordingly seen to be roughly coincident with ancient Breffney, embracing both Breffney O'Rourke and Breffney O'Reilly. Its first Bishops were termed Bishops of Breffny until after about 1454 when Andrew MacBrady was styled Bishop of Kilmore after erecting the parish church of St. Felimy (Fedlimid of Kilmore). St. Fedlemid, or Felim, who flourished in the early part of the sixth century, is the first known Bishop of Kilmore. Today the parrishes of Kilmore include Ballinaglera, Ballymeehan, Crrigallen, Cloonclare, Drumlease, Drumreilly Lower, Drumreilly Upper, Glenade, Inishmagrath, Killargue, Killasnet, Kinlough, and Oughteragh.
The former Diocese of Conmaicne, now the diocese of Ardagh (and Clonamcnois), may have been closely associated with Kilmore when they were both established at the Synod of Kells in 1152. The O'Ruairc (O'Rourkes) were lords over Conmaicne at that time. Today the parishes of Ardagh and Clonamcnoise include Aughavas, Annaduff, Bornacoola, Cloone-Conmaicne, Drumshanbo, Fenagh, Gorleteragh, Killenummery & Killery, Kiltoghert, Kiltubbred, and Mohill-Manachain.
Map of Kilmore

Diocese of Limerick - Limericensis

Based on an older territorial division, a Munster sub-kingdom ruled by the Ui Fidgente kings and later the O'Donovans, the Diocese of Limerick dates from the twelfth century when its boundaries were laid down at the Synod of Ráth Bressail in 1111. About 1195 the ancient See of Inniscathay or Inniscaterry (or part of it) was united with this bishopric. As stated above the ancient diocese of Inniscathy, comprised the Baronies of Moyarta, Clonderlaw, and Ibricken, in Clare; the Barony of Connello, in Limerick; and in Kerry, the ancient region of the Uí Fidgente. The ancient diocese of Inniscathay was probably divided among those of Limerick, Killaloe and Ardfert.
Parish List (and map)

Diocese of (Waterford and) Lismore - (Waterfordiensis and) Lismorensis

The Diocese of Waterford and Lismore is almost coterminous with the ancient Celtic territory of Decies (Déisi Mumhan). It comprises the County of Waterford (except five townlands) with a considerable portion (two baronies and part of two others) of Tipperary County, as well as a small area (12,000 acres) of County Cork. At the Synod of Rathbreasil (1111) the diocesan boundaries of Lisnore were formally aligned. It is thought the See of Waterford may not have been a separate diocese until the Synod of Kells in 1152. The ancient See of Ardmore was merged with Lismore soon after the arrival of the Anglo-Normans (after 1169). The diocese of Waterford (which included the city) was united with that of Lismore between 1358 and 1362.
Outline map of Waterford and Lismore

Diocese of Meath - Midensis

In extent it is the largest diocese in Ireland, and includes the greater part of the counties Meath, Westmeath, King's, and a small portion of the counties Longford, Dublin, and Cavan. The present Diocese of Meath anciently comprised eight episcopal Sees, including Clonard, Duleek, Kells, Trim, Ardbraccan, Dunshaughlin, Slane and Foure. At the Synod of Kells in 1152, all except Duleek and Kells were consolidated and the See of Meath was at Clonard. The See of Duleek became the centre of a diocese at the Synod of 1111, but in the late 12th century the Norman Bishop Simon de Rochfort had it merged with the diocese of Meath. Another account states that at the 2nd Synod of Cashel in 1172, it was decided to merge the Sees of Meath, as the province of Meath was granted to Hugh de Lacy. By 1202 the See of Kells had also been united into the diocese. In 1206, the first Norman Bishop of Meath, Simon de Rochfort, had the episcopal See moved from Clonard to Trim, where it remained until the reign of Henry VIII when it was moved to St. Mary's abbey at Ballymore.
The modern diocese of Meath was roughly co-extensive with the ancient territories of Midhe and Brega, which included many sub-kingdoms held by the southern Ui Neill, among others, up to the time of the Cambro-Norman invasion of the late 12th century.
The Annals of the Four Masters for 1174 record, "The diocese of Westmeath was annexed to the city of Clonmacnoise, by consent of the clergy of Ireland." The diocese of Clonmacnoise is still mentioned in this document for the year 1224. On the death of Peter Wall, its last bishop in 1568, the See of Clonmacnoise was annexed to the diocese of Meath by act of parliament.
Outline map of Meath

Diocese of Newry and Mourne

Sir Nicholas Bagenal in 1552 received a grant of practically the whole town of Newry and the lands surrounding it, and the Lordship of Mourne, which extended for ten miles in length and two in breadth. His ancestors, the Earls of Kilmorey, claimed exemption from the bishop's jurisdiction for his lordship of Newry, as having been extra-episcopal before the Reformation, although Newry is cited among the parishes under the jurisdiction of the See of Dromore in 1615, as it is among the Roman Catholic divisions. Today it is part of the Catholic Diocese of Dromore.
Location based on the Proni Diocese Maps

Diocese of Ossory - Ossoriensis

In the Province of Leinster, the ancient See of Ossory is bounded on the south by the Suir, on the east by the Barrow, on the west by Tipperary and King's County, and on the north by Queen's County. It corresponds geographically with the ancient Kingdom of Osraighe, whose first king, Aengus Osrithe, flourished in the second century of the Christian era. It comprehends most of the county of Kilkenny and the southwest portion of Queens (Leix). At the Synod of Rathbreasail (1111) the limits of the diocese were permanently fixed, substantially as they have since remained. At the same time the See was transferred from Seir-Kieran (named for the patron of Ossory, St. Kieran) to Aghaboe, but at the end of the twelfth century the See was transferred to Kilkenny city.
Parish Map of Ossory

Diocese of Raphoe - Rapotensis

The modern Diocese of Raphoe comprises the greater part of the Co. Donegal (Tirconail), with the notable exception of Inishowen which it at one time it had included. It was roughly co-extensive to the ancient territory of the Cenel Conaill, one of the leading tribes of the northern Ui Neill. Early successors to St. Eunan, its first bishop, were sometimes called Bishops of Ticonnel, from the name of the territory which the church of Raphoe is situated. In 1266, part of the diocese (Inishowen) was forcibly taken away by German O'Cherballen, Bishop of Derry. Raphoe (Gaelic, Rathboth, fort of cottages) was the first of St. Columba's Irish foundation to become an episcopal See. The monastery which he founded there in the sixth century was renovated about the year 700 by Adamnan, who succeeded him in Raphoe as well as in Iona.
Outline map of Raphoe

Diocese of Ross - Rossensis

St. Fachtna founded the See of Ross and his death occurred about 590. Formed in the Synod of Rathbreasail (1111), the boundaries of the Diocese of Ross appear to coincide with the lands of the O'Driscolls, chiefs of Corca Laoidhe. It was anciently referred to as Ross Alithri (or Elihir), and from its situation around the barony of East Carbery (Co. Cork), was called Rosscarbery [or Roscairbre]. The Roman Catholic diocese differs from that of the Protestant diocese by excluding the barony of Beare, which is included in the R.C. diocese of Kerry (Ardfert and Aghadoe). In 1581 Queen Elizabeth ventured to appoint a Protestant prelate under whom, in 1584, the Sees of Cork and Cloyne were annexed to Ross. However, in the Catholic arrangement Ross continued independent. In 1693, Bishop Sleyne of Cork was given Ross in commendam, and the See continued under his successors till 1748, when it was united to Cloyne under Bishop O'Brien. From 1748 Ross was administered by the Bishops of Cloyne, but it regained its autonomy under Bishop Crotty.
Parish map of Ross

Diocese of Tuam - Tuamensis

The Archdiocese of Tuam now comprises the territories of five ancient dioceses of Connacht mentioned at the Synod of Kells (1152), which at different periods were united to the original Diocese of Tuam. The current Diocese of Tuam extends, roughly speaking, from the Shannon westwards to the sea, and comprises half of County Galway, and nearly half of Mayo, with a small portion of south Roscommon.
The original See of Tuam, which may be taken as corresponding roughly with the modern deanery of Tuam, comprised the ancient territories known as the Conmaicne of Dunmore, and also the Ciarraigi of Loch nan-Airneadh, as well as a portion of Corcamogha and the Sodan territory. When the O'Conor kings of the twelfth century came to be the chief rulers of Connacht, they resided mainly at Tuam.
In the Synod of Rath Breasail (1111) the Diocese of Cunga (Cong) was counted as one of the five dioceses of Connacht, along with Tuam, Killala, Clonfert, and Ardcharne, but there is no mention of Cong at the Synod of Kells in 1152. It held jurisdiction over nineteen parishes in the Baronies of Ballynahinch, Ross, and Kilmaine. It is stated in the "Book of Ballymote" that Aodh, son of Eochaí Tirmcharna, King of Connacht, bestowed Enaghdún (Annaghdown) on God and St. Brendan of Cluain Fearta; and it is probable that the ancient See of Cunga was transferred to Enaghdún early in the twelfth century (1114?).
. The town of Galway originally belonged to the diocese of Eanach Dúin (aka Enaghdune or Annaghdown), an ancient bishoprick which included Connemara, and was united in 1324 to the archiepiscopal See of Tuam. The ancient See of Annaghdown grew out of the monastery founded by St. Brendan for his sister St. Briga. Its jurisdiction extended over Ui Briúin Seóla (O'Flaherty's country) around Lough Corrib and comprised in all some seventeen parishes. By other accounts the See was independent down to the death of Thomas O'Mellaigh in 1250 when it was merged with Tuam. It later was referred to as the Diocese of Galway, which united with the dioceses of Kilmacduagh and Kilfenora about 1866.
In 1152 the Diocese of Mayo was recognized by the Synod of Kells as one of the Connacht Sees, but was merged into Tuam about 1209 with the death of Bishop O'Duffy. At one time Mayo had no fewer than twenty-eight parishes under its jurisdiction, which extended from the Dalgin River at Kilvine to Achill Head.
The jurisdiction of the Diocese of Aghagower extended over the "Owles", the territory around Clew Bay, but at an early date it was absorbed first into the See of Mayo and afterwards into that of Tuam.
Kilmeen was the seat of a Bishop until 1152. It was then attached to the deanery of Athenry and when Athenry was placed under the jurisdiction of the Archdiocese of Tuam in 1351 so too was Kilmeen. It should be noted here that Kilmeen is an "island parish" of the Tuam Archdioceses. It is cut away from the rest of the Archdiocese and is completely surrounded by parishes of the Clonfert diocese.
Outline map of Tuam

Also see:
19th century Diocesan Boundaries
Map of current Catholic Dioceses
A list of current Catholic Dioceses (with links)
Compare the modern Anglican Church of Ireland Provinces
Local Catholic Church History and Genealogy

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