The McCanns, according to tradition, are a Milesian people descended from Colla-da-Chrioch, the first king of Orghilla or Oriel. The kingdom of Oriel encompassed the land from County Donegal to County Louth. Oriel is almost synonymous with Ulster. Colla-da-Chrioch, a southern conqueror of Ulster, was one of the three Collas. The identitiy of the folks who lived in Oriel is shrouded in mystery and disgreement among historians. Historians who give credence to thier existence, generally place Colla-da-Chrioch's conquest of Ulster in 331 AD. Some disagree placing it anywhere in the succeeding 100 years. Some scholars feel that the three Collas never existed. The McCanns are said to have descended from Breasail, a grandson of Colla-da-Chrioch.

This notable Irish surname is an Anglicized form of the Old Gaelic "MacCana", a patronymic of the personal byname "Cana", from "cano", wolf cub. Traditionally, Irish family names are taken from the heads of tribes, revered elders, or some illustrious warrior, and are usually prefixed by "Mac", son of, or "O", denoting "grandson, male descendant of.

Ireland was one of the earliest countries to evolve a system of hereditary surnames. They came into being as early as 1000. The tradition of surnames in Ireland developed spontaneously, as the population increased and the former practice, first of single names and then of ephemeral patronymics or agnomina of the nickname type proved insufficiently definitive. At first the surname was formed by prefixing 'Mac' to the father's Christian name or 'O 'to that of a grandfather or earlier ancestor. At first the coat of arms was a practical matter which served a function on the battlefield and in tournaments. With his helmet covering his face, and armour encasing the knight from head to foot, the only means of identification for his followers, was the insignia painted on his shield and embroidered on his surcoat, the flowing and draped garment worn over the armour. The surnames in Ireland originally signified membership of a clan, but with the passage of time, the clan system became less distinct, and surnames came to identify membership of what is called a 'sept'; a group of people all living in the same locality, all bearing the same surname, but not necessarily descended from a common ancestor. Adoption of the name by people who did not otherwise have a surname and by dependents was not uncommon. Just over one hundred years after the Norman Conquest of England, the first Normans arrived in Ireland. Richard de Clare, Second Earl of Pembroke (died 1176), was known as Strongbow. He was invited to Ireland by Dermot MacMurrough, King of Leinster, whose daughter he married, to help him in his wars with his neighbours. He was accompanied by several retainers whose names, like his own, have become well established as surnames in Ireland. The Normans established themselves in Leinster and paid homage to Henry II of England. Some of the Norman settlers acquired surnames derived from the Irish.

It is well accepted that the McCanns originated on the banks of Lough Neagh; they were called the lords of Clan Breasail. Over time, this district was sometimes referred to as Clanbrassil, and Breasal Macha and was located on the southern shores of Lough Neagh. On a present day map Breasal Macha would cover the current baronies of Oneilland East, Oneilland West and Middle Dungannon. The first two are located in present day County Armagh and the third in County Tyrone. These geopolitical divisions (counties) were not created until late in the sixteenth century and therefore did not exist in the early days of the McCann clan. Notwithstanding this fact, McCann is thought of as a County Armagh sept.

The territory of this great sept lay on the southern shores of Lough Neagh, originally occupied by the O'Garveys. Several members of the sept are described in the "Annals of the Four Masters"; the last to be mentioned in the Annals was killed in 1260. Donnell MacCanna, Chief of Clanbrassil, was recorded in 1598, and the surname is still widespread in the vicinity of Lough Neagh, though uncommon elsewhere.

The McCann surname is considered to be among the earliest hereditary surnames in the world. Of course at the time of Colla-da-Chrioch's grandson, surnames were not in use. Ireland was one of the first countries in Europe to adopt the use of hereditary surnames. It has been claimed by the late Edward Lysacht, the famous Gaelic etymologist, that O'Clery (O' Cleireach) was one of the earliest of all surname recordings anywhere in the world, dating from the 10th century. The surname McCann began to be used in the 12th Century. Its original form was Mac Cana and it means "son of Cana", which was the given name of an early McCann chieftain a personal name meaning 'wolf cub' The surname has taken many forms over the years: MacCann, Macann, Macan, McCan, McGann, Mac Anna, MacCanna, Cann, Canny, McCanney, Macan, Makan, Mican, and McKann.

Historian, John O'Hart, in his Irish Pedigrees, lists Cana (Annadh) as a younger brother of Donal, who is number 103 on the McMahon, of County Monaghan, pedigree and as an ancestor of the McCanns. The following is O'Hart's account of the McCann pedigree.

Mc Cann Pedigree

103. Cana: son of Maithgamhuin; a quo MacCana

104. Cana Mor McCan: his son; first bearer of this surname

105. Cana Oge (younger): his son

106. Cathal McCann: his son

107. Cathal: his son

108. Hugh the Valiant: his son

109. Terence, the Wine Drinker: his son

110. Donal: his son; lord of Clanbreasail

111. Hugh: his son

112. Cairbre Oge: his son

113. Neal: his son

114. Neal Oge: his son

115. Cairbre Mor: his son

116: Hugh Mor: his son

117. Hugh Mor: his son

118. Terence, of upper Clanbreasail

119. Cairbre: his son

120. Brian Buidhe (flaxen haired): his son; lord of Upper Clanbreasail

121. Lochlann: his son; lord of Clanbreasail

122. Cormac, lord of Clanbreasail

123. Brian Ruadh (red haired): his son

124. Glaisneach McCann; his son; had a daughter named Elizabeth, who was married to John Hamilton, by whom she had six sons: one of which was killed in the Battle of Aughrim, on the 12 of July, 1691.

On June 18th 1599 the marriage of Mary McCann and Michael Rilie is recorded in Adamstown, Co. Wexford. Ithe McCann name occurs frequently in Ulster Church Registers during the 18th and 19th Centuries. An interesting namebearer was Michael Joseph M(a)cCann (1824 - 1883) author of the celebrated poem 'O' Donnell Abu'. Charles, son of John and Sarah Canny was christened on September 17th 1704 at St. Botolph without Aldesgate, London. The first recorded spelling of the family name is shown to be that of Amhlaibh Mac Canna, a 'pillar of chivalry and vigour of Cinel Eoghain' i.e. a clan name, which was dated Deceases 1155, 'The Annals of the Four Masters', during the reign of High Kings of Ireland, 'with opposition', 1022 - 1166. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to 'develop' often leading to astonishing variants of the original spelling.

On October 11th 1687, Patrick McCann and Ann McBride were married at Clones, County Monaghan. The famous poem "O'Donnell Abu" was written by Michael Joseph MacCann (1824 - 1883), and seventy-eight persons bearing the name McCann appear on a "List of Irish Famine Immigrants Arriving at the Port of New York", between the years 1846 to 1851. A Coat of Arms granted to the M(a)cCann family is an azure shield with gold fretty, on a silver fess a red boar passant, the Crest being a salmon naiant proper.

There were about 1900 McCanns listed in the Griffiths Valuation. About a fifth of these of these were in County Armagh, and half of all McCanns were found within the four counties of Armagh, Antrim, Tyrone, and Down. About one out of every 500 Irishmen was a McCann. The map of Co Armagh shows that most of the McCanns were living along the southern shore of Lough (Lake) Neagh - with the greatest concentration of them in the civil parish of Drumcree. McCanns are probably as thick as leaves on the ground in the town of Portadown, Co Armagh and the name of McCann continues to this very day.