The O Beirnes are predominantly Gaodhail (Milesian) Celts but with blood of the Fir Bolgs (Belgae) and probably of those Norwegian Vikings who settled on the banks of the Shannon where the O Beirnes were and who supposedly gave them their surname. From historic times some also must have blood of the French or Spanish and many of the English. Despite these mixtures there is a belief in the existence of a characteristic “Beirne Look,” largely indefinable but including a straight nose. This could have some basis in fact because, as shown below, the O Beirne Sept was geographically isolated for longer than most other small septs and thus could have retained distinctive have physical characteristics more readily. Personal characteristics that have been attributed to them are actually more generally Irish than specific to the family: a liberal and amiable integrity, better abilities at handling people than money or properly, tendencies to be stubborn when they believe themselves to be in the right and to remember injustices and humor. The validity of these perceptions may be judged from the portraits and biographies of the individual O Beirnes. More factually, some have remarkable abilities with foreign languages and many have writing abilities.

The O Beirne homeland was Tir Briuin, or Úi Briúin,  na Sinna, or Sionna, an area of 30 or 35 square miles in the Barony of Ballintober North in northeastern County Roscommon, between the Shannon and Elphin. It approximates the parishes of Aughrim, Kilmore and Clooncraff. It was more or less cut off by water: to the east and north by the Shannon and its lakes; to the west and southwest by an extensive region of connecting lakes, rivers, marshes and bogs known as the North, or Great, Swampy Plain. It supposedly was named after Brión, son of Eochaida Mugmedon, King of Connacht around the year 400 and himself son of a King of Ireland. Muirheadhach Muillethan, King of Connacht who died  in the year 701 was a descendant of Brión and the founder of a dynasty known as Sil Muirheadhach, or Sil Murray, which in Tir Briuin included the O Monaghans, O Hanlys and Mac Brenans, who claimed descent from Brión, and the O Beirnes, who may have moved into Tir Briuin later. Others of Sil Murray were the Mac Dermots (Kings of Moylurg who were supported by the O Beirnes), the Roscommon branches of the O Conors (Kings of Connacht and sometime of Ireland when the O Beirnes were their supporters), O Mulconry, or Conry (who were later arrivals), O Flanagans, Mac Manuses, Mac Geraghtys, O Flynns, and others. Fiachra, brother of Brión, was the origin of the eventually more powerful dynasty of Ui Fiachrach which included an O’Beirne sept. The legendary, Niall of the Nine Hostages (d. 405) was a half brother of those two.

O'Beirne Country

            Tir Briuin was a tuath which was a petty kingdom controlled by a particular sept or tribe, in this case first by the O Monaghans (O Mannachain) for some five centuries until they were ousted by the O Beirnes around the year 1300. The O Monaghans had taken control of two adjoining tuaths: that of the O  Hanlys to the south along the Shannon and including the Slieve Bawn Hills; and that of the Mac Brannans (O Brennans), and earlier of the O Mulvihills which included the North Swampy Plain. This made the O Monaghan Chieftain the Lord or ‘”King” of the Three Tuaths, a descriptive courtesy title that the O Beirne chieftains inherited in 1287.
            Tir Briuin was part of a Gaelic enclave consisting of Roscommon and parts of Galway and Sligo that was regarded with justification by the English as remote, primitive, lawless, and much given to tribal feuding and plundering. Consequently it was largely ignored for some 300 years while most of Ireland was, relatively speaking, subdued and colonized. Tir Briuin was a backwater within a backwater where the O Beirnes were isolated by terrain, by politics, and by poverty for longer than most Irish septs. The lifestyles, habits, customs, and beliefs of the inhabitants of the region are described in Dermot Mac Dermot’s comprehensive and scholarly history Mac Dermot of Moylurg (1996).
             There was a small but well-off separate Sept in Mayo in the 1400s to 1600s, the Ó Birns of Ciera and of Faichrach’s Race which had extensive estates in Robeen parish (also noted for a ford that was haunted by fairies) north of Ballinrobe. They seemingly became Byrne or O’Byrne and disappeared. Rathlin-O’Beirne or Rathlin O Birne is the name of an island in the Atlantic off the extreme southwest point of Donegal in what was Mac Sweeney territory. How it got that name could not be discovered but it may be significant that both O Beirne and Mac Sweeney heraldic arms feature a lizard. Two early O Beirne colonies in eastern Ireland may originally have been O Byrne: those in Kildare in the 1100s and 1700s and of whom more later; and a family in County Down in the 1600s.

The O Beirnes were a Sept when they were confined to Tir Briuin. They evolved into a family as they dispersed outward. The Sept or Family was headed by a Chieftain. This position was usually hereditary but not necessarily or always. The purported genealogy of O Beirne Chieftains as given in the Annals of the Four Masters begins with Aodh Balbh, or Hugh the Stutterer, who was either a son of the 23^rd King of Connacht or himself the 26^th King. Early branches from the main O Beirne line became Balfe, Wood, Hoban, and Barnewell as western Ireland names (they also had separate origins elsewhere in Ireland or in Britain), and Fallon.  
            By the 1600s the O Beirne Chieftainship had status as one of the 86 then recognized as such according to C.E. Swazey in The Irish Chieftains (1974). But it is not one of the 16 that are recognized today. The genealogy of the early O Beirne chieftains in the Annals of the Four Masters evidently is partly contrived as it differs from the dated references to deeds or deaths of specific individuals in, e.g., the Annals of Connacht. Information from most of the 1600s and 1700s is only fragmentary, though three genealogies were found:-

The origin of the name O Beirne is obscure. One suggestion was that it originated from a Beirin who was about the sixth Chieftain in line after Aodh and whose son thus was Ó Beirin. This is improbable because the spelling O Beirn or O Beirne did not appear until the 1700s, five or six centuries after the original Beirin and evolved from Ó Birn into Ó Birne and Ó Berne.  Another suggestion was that its origin was from Björn, the name of a Viking who supposedly settled on the banks of the Shannon and gave his name to a sept already there. Norsemen from Norway are said to have controlled the Shannon and its lakes for a time; and they evidently occupied Tir Briuin as in the 930s they plundered Moylurg, a Mac Dermot territory to the northwest that approximated the present Barony of Boyle, and the Slieve Bawn area to the south of Tir Briuin. This raises the possibility that the O Beirnes were originally of Viking origin rather than Celts. Perhaps O Beirnes derived their name from that of the district where they settled: Birn  from Brión or Briúin.

O Beirne is used in this memoir as the generic name for the Family and for individuals who are not specified as having other versions of the name. Beirne is now so widely used that it would he futile to try to replace it with the more correct Gaelic Ó Beirn.
There are many variants. The prefix may be Ó (originally Ua), O', O, missing, or combined with the name (as in Obeirne). The first vowel may be an e (as in Bern or Berne which has origins additional to O Beirne, Beren, Beirn, Beirin, Beirne, Beirnie, Berrane, Beryne), an i (as in Biern, Bierne, Birn, Birne, Biranne, Bireen, Birrane), an a (as in Barn), or a y as in Byrns, Byrane, Byron). The middle letters may be fused (as in Beimes). There may be a terminal s (as in Beirnes, Beirns) or ss. The whole name may be changed into a similarly-sounding one such as Hoban, Oberon, Bruin. It may be replaced by a more generally familiar and similar-sounding one such as the Irish O'Byrne, Byrnes or Byrne (frequently), the Scots Burn or Burns, the English Barnes, or the Jewish Bernie (commonly  when misread and then spoken). Other names that are not variants of O Beirne include the English Bruen or O'Bruen as a West of Ireland name, the Scots Birnie and the German Behrens. Apart from by marriage, non-O Beirnes sometimes adopted the name: mercenaries and servants in early Ireland customarily took their leader's name; and evidently some slaves in the Southern States of America took the name of their Beirne owners and Australian aborigines the name of their Beirne employers.
            All this illustrates the impossibility of making a comprehensive and balanced review of O Beirne accomplishments as too many who were originally O Beirnes cannot now be identified as such. One example of what could happen: three sons of a Francis O'Beirne from Carrick-on-Shannon became in America Byrnes, Byrne, and Burns.  
            Predominantly it was recorders who changed spellings. Early recorders of births, marriages and deaths in rural Ireland who were semi-literate or worse tried as best they could to write down what they heard. Early English recorders who, to give the most acceptable explanation, were unfamiliar with the accent on the Ó assumed that it was a misplaced apostrophe and thus made each Ó an O'. Officials in Ireland in the 1800s and early 1900s deliberately tried to Anglicize Irish surnames by omitting the O' and the Mac from birth certificates. Overworked, undereducated or indifferent North American immigration officials wrote down what they thought they heard from immigrants speaking English with thick accents or not at all or deliberately Americanized names that looked too foreign for their liking. And even now some supposedly more literate authors and editors do not appreciate that a maxim of English spelling, i before e except after c, is not applicable to names of Gaelic origins and thus convert Beirne into Bierne.  
            Individual O Beirnes changed their own names. Some did so in Ireland (and often also turned Protestant) by dropping the O' in an attempt to be perceived by English invaders as not antagonistic and thus to avoid being expropriated. Many dropped the O' while emigrating to try to avoid being recognized as too obviously Irish and Catholic in destinations where there was prejudice and discrimination, which is the main reason why most O Beirnes in Britain and America lack the O'. After emigrating some gave up trying to spell out their unfamiliar name, or their employers did, and accepted being called Byrne or Burns. But in the early 1800s in Ireland and the later 1900s in both Ireland and America some O Beirnes have reclaimed lost aspects of their heritage by resurrecting the Ó, O' or O and sometimes also reverting to early Gaelic spellings; and some whose surnames are not O Beirne but who have had a Beirne in their ancestry have adopted it as a first or middle name.

Heraldic arms belong to the individual who was granted them and his  descendants and can be exhibited by his supporters. According to the definition used by the Office of the Chief Herald of Ireland (in the Irish Genealogical Office, established in 1943), the arms of a Clan or Family are those of the last Chief of the Name who was duly inaugurated under old Gaelic laws. On that basis it is not at this time possible for the O Beirne Family heraldic arms to be identified unequivocally, as seemingly it is not now known who was the last so inaugurated O Beirne Chieftain; anyway the known genealogy of the Chieftains has too many gaps and inconsistencies to enable lineal descendants to be identified positively.  

While most Families and Clans have specific heraldic arms the O Beirnes clearly do not. This could be a reason why they are not figured in Grenham's Clans and Families of Ireland (1993). Apart from the four known versions each can have variations on its basic pattern, as figures here show. To be realistic there is in fact nothing to prevent any O Beirne from displaying any version to which he feels affiliated, provided that it is not the arms of a different Family or Clan. Extreme examples are a recent Canadian version which has in place of the tree and lizard a maple leaf and beaver and the motto Dissentio Urbanitas, and an Australian one with a gum tree and kangaroo and the motto Dies Commodus, Propinquus.

 The O Beirnes showed no significant abilities to enrich and augment themselves and their property in the internecine feuds except once in the later 1200s at the expense of the O Monaghans. Constantly suppressive to their health and survival were effects of the primitive living conditions, poor nutrition, especially before the time of the potato, and worse hygiene and the frequent extremes of natural disaster, famines and epidemics. These were aggravated and intensified by the cold, wet climate of the Little Ice Age of the 1500s to 1800s which happened to coincide with the times of greatest oppression and suppression by the English. All this meant that especially from the 1500s onwards O Beirnes had to concentrate their energies on defending, subsisting, and surviving. The centuries of natural and enforced population suppression meant that those who survived had to be tough. This doubtless contributed to the ability of their descendants to succeed when given the freedom and opportunities overseas. 

Emigration has determined the history of the O Beirnes more than any other single influence. About two-thirds now live outside Ireland. From the 1600s into the 1900s O Beirnes emigrated primarily to escape from intolerable living or political conditions in Ireland and in the hope of finding better conditions abroad. As they became increasingly well educated in recent years it has been more in the expectation of finding better employment and career opportunities abroad than were available to them in Ireland.

Ireland they spread south and southeast in Roscommon to the Strokestown, Tulsk, and Castleplunkett districts, west via Elphin to Frenchpark and beyond, north and east into southern and western Leitrim and northeastern Longford and further eastwards to the Dublin district via Westmeath and Meath.  

    Emigration to Britain was especially at times of economic stress and food shortages in Ireland. It continued through the 1800s and 1900s. Much of it was temporary. Military O Beirnes -the so-called Wild Geese - went to France and Spain in the 1600s and early 1700s; and O Beirnes joined up for all Britain’s wars up to and including World War II.  
            O Beirne emigrations to North America did not begin significantly until the 1800s, then increased, and after the Famine of the 1840s became a flood that continued into the 1900s, dampened every now and again by American economic depressions, wars, and immigration restrictions. The patterns to Australia and Canada were similar.