"There is much confusion regarding these names and I wanted to create a clear picture of how they are (or are not) inter-related. Many people bearing these names have been ripped off because some commercial heraldic companies refuse to consider the fact that there are several septs and also several distinct coats of arms. Almost invariably they will supply the arms of MacMahon of Thomond to any McMahon, Mahon and even  O'Mahony without any regard to their ancestry. Perhaps this modest effort will help to compensate. I have to admit that there are some strange similarities among the coats of arms which I cannot explain. The two most obvious are the sword piercing the fleur-de-lis in the crests of both O'Mahony and MacMahon of Oriel, and the blue lion rampant on a gold field that feature on both the arms of (O) Mahon and (O) Mahony."

The Two Septs of Mac Mahon

MacMahon - originally Mac Mathghamha, but in contemporary Irish, Mac Mathúna, is one of the best known and distinguished surnames in Ireland. It has to be said that some Mahons may be really MacMahons who simply dropped the prefix. However, as we will see later, most Mahons are of different stock. The name is patronymic in nature, from the personal name Mathghamhain, which itself is taken from an old Irish word for a bear (see our analysis of the meaning of the name). There are two distinct septs of MacMahon, each descended from a different Mahon.

The first of these is Mac Mahons whose chiefs were lords of Oriel. They reputedly descend from Cairbre an Daimh Airgid (the learned and wealthy), grandfather to the Three Collas. Cairbre was of the line of Kings of Oriel who descended from Conn of the Hundred Battles.

Secondly, we find the sept of Mac Mahon of Thomond, whose territory, Corcabaskin, was adjacent to the O Briens of Thomond in County Clare and indeed they are "cousins" to the O'Briens, being descended from Mahon who was the son of Murtagh Mor, an O Brien king of Ireland who died in AD 119. The Corcabaskin MacMahons' last chieftain died after the battle of Kinsale, accidentally killed by his own son.

Between them, these two septs account for about 10,000 of the name today in Ireland, and still very much at home in their respective ancestral territories.

The last chieftain of the Ulster MacMahons of Oriel, Hugh Oge MacMahon (1606 - 44), was a lieutenant-colonel in the Spanish army. He inherited a rich estate in County Monaghan and when he returned home in 1641 he became involved with Conor Maguire in the conspiracy to capture Dublin Castle. They were betrayed by Owen O Connolly who had won their confidence. For several years they were imprisoned in the Tower of London. Making a brief escape, they were discovered hiding in Drury Lane and were charged with high treason and executed in 1644.

Probably the most colourful character in the annals of the MacMahons of Thomond was a woman, Maire Rua (rua meaning red), daughter of Turlough MacMahon. She was notorious for the number and variety of her husbands and lovers. Contemporary historians have purged her reputation and it seems she had but three husbands. Born in about 1615 in County Clare to an O Brien mother, she was married in her teens to Daniel Neylon, who died young. Next she chose Conor O Brien and together they built the still handsome, though ruined castle of Lemaneagh at the edge of the Burren district in County Clare. When he was killed in the Cromwellian wars, Maire, to protect her eleven children and her property, married a Cromwellian soldier and raised one of her sons a Protestant. She was indicted for murder but was pardoned. As a strong-minded woman of the west of Ireland, reminiscent of Grace O Malley, it is easy to see how she, too, entered the realms of folklore.

The remains of Carrigaholt Castle dominate the harbour at Loop Head in County Clare. Teige MacMahon (died 1601), the last of the lords of Corcabaskin, lived here and must have witnessed the ships of the Spanish Armada pause here in 1588. Later, Carrigaholt fell to Sir William Penn, father of the Quaker founder of Pennsylvania.

When there was no longer any point in fighting at home for their own land, many of these MacMahons fled abroad. In the lists of the Irish Brigade in France their name constitutes a litany of high-ranking officers. In 1763, Louis XV wished to ennoble John Baptiste MacMahon (1715 - 80), but John had to verify his descent from King Brian Boru before he could be titled Marquis d'Eguilly!  His son, Maurice Francis MacMahon, suffered greatly for his royalist allegiance during the French Revolution. He died in 1831 leaving seventeen children. One of these was Edmonde Patrice MacMahon (1808 - 93), who was to become a Field Marshal and President of the Republic of France. Like his ancestors in Ireland, and later France, he was a professional soldier. It was General MacMahon who led the victorious French at Sebastopol. When he captured the Malakoff fortress and was told to leave it (it was mined) he retorted, "J'y suis, j'y reste" (here I am and here I stay). He was the hero of the day and was created Duke of Magenta. During his six-year presidency, his royalist feelings made it difficult for him to control the rabidly republican French of the 1870s. At Ardmore in County Waterford there is the ruin of a gingerbread castle known as Ardo or Ardogena which was inherited by General MacMahon. Having little use for it, he sold it in 1874 to the McKennas. The palatial Chateau de Sully near Bordeaux, home of Philippe MacMahon, 4th Duke of Magenta and direct descendant of the nineteenth-century President of France, is by no means a ruin. The Duke proudly shows visitors the 18-carat gold sword presented to his ancestor by the people of Ireland in 1860. Both he and his wife have a deep interest in Ireland and attended a ceremony held in Limerick commemorating the scattering of the "Wild Geese".

The MacMahons proliferated in Australia. Gregan McMahon (1874 - 1941), son of Irish parents, was born in Sydney and was a brilliant student. He forsook a legal career for acting and producing. The Gregan McMahon Players staged many of the classics and toured Australia. Sir William McMahon (b. 1908) was Prime Minister of Australia from 1971 to 1972.

Scholars have reached the conclusion that the notorious Charles Patrick Mahon (1800 - 91) who called himself "The O Gorman Mahon" was of the Clare MacMahons. A flamboyant soldier and politician he quarrelled with Daniel O Connell. Spurning a career in law, he embarked on one which took him all over the world. He became an intimate of Louis Philippe and Talleyrand in France. The Czar of Russia appointed him to his bodyguard. He soldiered in the Far East, South America, was an admiral in the Chilean navy, a colonel in Brazil's army and a colonel in Napoleon III's regiment. He re-entered politics in Ireland as a supporter of Parnell. He unwittingly led to the downfall of Parnell by introducing him to Katherine (Kitty) O Shea. The hero of thirteen duels, many of them fatal to his opponents, he died in London at the age of 91, vigorous to the last, although it is not possible to authenticate all his adventures.

The MacMahons are almost as widespread in the United States as they are in Ireland. Bernard MacMahon (died 1816) was driven there by the state of Irish politics. He settled in Philadelphia, where he made his name in the cultivation of rare plants. Helped by his Irish wife he built up one of the biggest seed businesses in the United States and had the evergreen shrub, Berberis mahonia, named after him.

Mahon and O'Mahon

The name Mahon is often assumed to be a contracted form of MacMahon, the original Irish form of which was MacMathghamha, modernised to MacMathuna. While this is sometimes true, Mahon is more often an anglicised form of Ó Mocháin or Ó Macháin which is also found as Mohan, Maughan, Mahan and even Vaughan, although this last name is also an import from Wales.

There are two septs of the name. In Galway, the form Mohan was formerly common, but has largely been replaced by Mahon. It is believed that this Galway sept migrated southward into Munster, where the name took the form Vaughan. Ballyvaughan in County Clare is known in Irish as Baile Uí Bheachain, i.e. Behan's Town, however, given that Behan is a midland name, most historians believe that it should more rightly be Baile Uí Mhacháin i.e. Mahon's Town, as the Galway Mahons were centred just a few miles to the north. One of the septs of MacMahon was centred in County Clare and its proximity to the Ó Macháin sept has resulted in inevitable absorption, interchange and confusion.

Another sept of Ó Macháin is much more clearly defined. This is the sept of Kilmacduagh and they occupied territory in north Roscommon and Longford. This group, also known as Ó Mocháin and Ó Macháin were once of considerable importance and were known as Mahon, Mohan and Moghan, but never Vaughan.

By the eleventh century, in the average church, the abbot, generally known as the "comharba" (anglicised as "coarb" and meaning "heir"), of the saintly founder, or, if it were not the saint's principal establishment, the "airchinnech" (anglicised as "erenagh" and meaning "head"), had become a lay lord, whose family held the office and the church property from generation to generation. In some cases, apparently, all trace of a church establisment had disappeared, except that the incumbent claimed for his lands the "termonn" of the ancient monastery, those privileges and exemptions which had from old been accorded to ecclesiastical property. But generally the coarb or eneragh maintained a priest. These Mahons were hereditary erenaghs (religious administrators) of Killaraght and keepers of the cross of St. Attracta.

Of this sept was Gregory O'Moghan, Archbishop of Tuam from 1372 to 1385, who died in 1392.

The town of Ballymahon, in County Longford, takes its name from this family. The senior male line of the Roscommon family seems to have expired with Denis Mahon, of Strokestown, County Roscommon. His daughter and heir, Grace Mahon, married Henry Sandford Pakenham, who assumed the additional surname and coat of arms of Mahon in 1847. The Pakenhams held the title of Earls of Longford through marriage into the Aungier family. The Mahons held the title of Baron Hartland in their own right, but this title became extinct in 1845.

There is also a Norman family, originally de Mohun but more recently just Mohun, also found in Ireland as well as parts of England. This name has also become Mohan and thence Mahon etc.

The (O) Mahons of Galway, do not appear to have borne arms, but those of Roscommon and Longford certainly did and these are well documented as are those of the de Mohun family.

(O) Mahony

The name Ó Mathghamhna - in modernised spelling O'Mahuna - is derived in the same way as MacMahon above. In this case Mathghamhan or Mahon in question was son of Cian Mac Mael Muda, the tenth-century warrior-prince, and Sadbh, daughter of the High King of Ireland, Brian Boru. Mathghamhan's ancestors were known as the Eoghanacht Raithline, a branch of that great group of dynasties claiming descent from Eoghan Mor, son of Oilioll Olum who, in the second century was reputedly first King of Munster. The O Mahonys occupied a huge tract of Munster, stretching from the environs of Cork city to Mizen Head. The sept owned this land until the seventeenth century when, in common with other Gaelic families in those stormy times, they were dispossessed. Today, many of their descendants continue to thrive in the land of their ancestors. Many more are scattered across the face of the earth with little or no knowledge of their origins, only recognising a link with Ireland through their surname.

During the clan wars of the Middle Ages, the O Mahonys divided into eight separate septs and at one time they owned fourteen castles in west Cork. Among their strongholds were Castle Mahon, Castle Lac, Dunmanus, Laemcon, Rosbrin, Ardintenant, Ballydevlin, Dunbeacon and Templemartin, the cradle of the clan near Bandon. Dun Lacha, near Mizen Head, was built in 1212 by Donagh na hImrice (Donough of the pilgrimages), so called because he went to the Holy Land. Ardintenant Castle beside Roaringwater Bay was the seat of the chief of Iveagh. At Rosbrin in the fifteenth century, the scholar-prince Finghin O Mahony translated Sir John Mandeville's book Travels in the Holy Land into Irish. Finghin's manuscripts were discovered in 1869 in the public library at Rennes in Brittany, where many Irish families fled following the catastrophic defeat by the English at the battle of Kinsale in 1601. According to an account by the O Mahonys of Lota Beg, Cork, "they held distinguished military and diplomatic appointments in the service of Continental sovereigns, and became allied by marriage with the nobility of France, Italy and Spain".

The most renowned of the Continental O Mahonys was Count Daniel O Mahony (died 1714), the hero of Cremona who commanded the Regiment of Dillon in the absence of its commander, Colonel Lally. Daniel, a direct descendant of Teigue O Mahony, the sixteenth century seneschal of Desmond, later gave a graphic account of his victory to an appreciative King Louis XIV.

It was Colonel John O Mahony (1815 - 77) who gave the name Fenian to the revolutionary brotherhood founded in the United States to assist in the liberation of Ireland. Descended from the O Mahonys of Kilbehenny in County Limerick, his political views forced him to flee to America. In New York he translated the great documentary record of Irish history, Geoffrey Keating's early seventeenth-century manuscript, Foras Feasa ar Eirinn (History of Ireland), indebting himself to future scholars. John O Mahony was the leader of the Fenian Brotherhood, and, during the American Civil War, he organised a regiment of Fenians, the 99th Regiment of the New York National Guard, of which he was appointed colonel. Despite his patriotism, he was too scholarly to be a successful leader, so he devoted his life to scholarship and campaigning on behalf of his beloved country, raising £8,000 for that cause. He died in poverty in New York, too proud to ask for help for himself.
Probably the most celebrated O Mahony was known as Father Prout. He was born Francis Sylvester Mahony (1804 - 66), second son of Martin Mahony of the woollen manufacturing dynasty of Blarney. Educated in France and Rome, he was destined for the Jesuit priesthood, but was rejected on grounds of ill health. Instead he became a literary and somewhat Bohemian priest who wrote verse and became a journalist, using the pseudonym Father Prout. A traveller and bon viveur, he numbered among his acquaintances Thomas Moore, Charles Dickens, Lady Blessington (see Power) and William Makepeace Thackeray. He wrote the words of the haunting song about Cork city:

The bells of Shandon,
which sound so grand
on the pleasant waters
of the River Lee.

Canon John O Mahony (1844 - 1912) wrote the History of the O Mahony septs of Kinelmeaky and Ivagha:

The O Mahony of Kerry moved to County Wicklow, where he established his family at Grange Con. His son, Pierce Gun Mahony, barrister and Herald of Arms, was unwittingly involved in the scandal of the Irish Crown Jewels which disappeared from the Genealogical Office in Dublin Castle just before the visit of Edward VII in July 1907. It was a most unsavoury affair Pierce Mahony's uncle, Sir Arthur Vicars, Ulster King of Arms, was dismissed ignominiously and, in 1921, his home was burned down and he was murdered. Pierce Gun Mahony was found drowned in Grange Con Lake in 1914. While there were many suspects, no one was brought to trial for the theft and there is little hope that the jewels will ever be found, although occasionally people come forward announcing that they know where they are!

In 1870 a farmer's son, John O Mahony, ran away from Kilcrohane in west Cork, at the age of 17, and emigrated to America to seek his fortune. He rose to become the "Senator from Wyoming" and, for his enterprise as a rancher, engineer, oil prospector and banker, was dubbed "King of the West".

David J. Mahoney, chief executive of the Norton Simon Corporation, whose personal wealth has been put at $10 million, was born in the Bronx, the son of an Irish crane driver. He progressed, via a basketball scholarship, an army commission and advertising, to become a leading businessman in the United States. He is nicknamed "the Kissinger of Commerce".

The twentieth century produced the most lovable O Mahony - Eoin O Mahony (1904 - 70). One of the O Mahonys of Dun Locha, Douglas, County Cork, he was barrister, Knight of Malta, genealogist, raconteur and a world traveller. It was he who originated the annual O Mahony rally in 1955. He has been described as "a maker of epics, an interpreter of history, an incurable romantic, the avowed champion of lost causes, a sterling protagonist of the social values of rural Ireland with a mission of preservation of 'resistance to materialism' he was a modern crusader.

The O Mahony name, originally the Irish word for bear, has been modernised to O Mathuna. Padraig O Mathuna, the Cashel artist who works in silver and enamel, made a commemorative cup for Eoin O Mahony and described him as "a catalyst fusing ages through scholarship and genealogy, linking our continuity with our oldest past". Alas, Eoin left little of written family history, only the tapes of his weekly programme for Radio Eireann, Meet the Clans.

An unexpected, and probably unsuspected, member of the clan is the audacious television comedian, Dave Allen. Born David Tynan O Mahony, he was the third son of the Dublin newspaper journalist G.J.C. (Pussy) Tynan O Mahony who became general manager of the Irish Times.

The clan's chief representative on the Continent, Vicomte Yves O Mahony of Orleans, France, retains links with Ireland. A barrister, he is directly descended from Sean Meirgeach (freckled) O Matgamma of Dunloe, who died about 1720.

Fishermen, farmers, teachers, shop owners, priests, doctors, lawyers, nuns, nurses, journalists - the numerous O Mahonys are scattered all over west Munster. On the Bandon (County Cork) electoral role there are 800 O Mahonys.

The O Mahony Records Society sponsors an annual scholarship of £1,000, administered by The Royal Hibernian Academy, to enable scholars to go abroad to research sources of Irish family history.

Father Francis O'Mahony, Provincial of the Irish Franciscans from 1626 to 1629, was also known as Father Francis Matthews. Matthews is rare as an anglicised form of O'Mahony, but not unusual in Ulster as a synonym of MacMahon.

Mac Ardle, Mac Phillips, Mathews

I'll add more information on how these surnames developed from MacMahon as I am able to track that information down....

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