๐ How Rare Are You in Ireland?
๐ฎ๐ช Genetic Landscape of Ireland
Ireland holds one of the world's most distinctive genetic profiles. The Irish have the highest rate of red hair on Earth (~10%), the highest frequency of O blood type in Europe (~55%), and an unusually high rate of Celtic genetic markers (R1b haplogroup) found in ~80% of Irish men. Ireland's island geography created a genetic bottleneck that preserved these rare traits. The phrase 'Black Irish' refers to dark-haired Irish people, whose features may trace to Spanish Armada survivors or pre-Celtic inhabitants.
The island's story is as much about who left as who stayed. Emigration after the Famine of the 1840s ran so heavy that the population is still below its pre-Famine peak, and the people claiming Irish descent abroad vastly outnumber those living here. What remained is legible in the surnames. ร and Mac mean descendant of and son of, and the families they name stayed put long enough that Ryan still clusters in Tipperary, Murphy in Wexford and Cork, and O'Sullivan across Kerry and west Cork. Anglicisation stripped the prefixes from many of them during the nineteenth century, and the twentieth put some back. Ulster carries a separate layer of Scottish and English names from the plantation era, which is why the north reads differently in a phone book.
๐ค The Accent That Splits Seรกn From Sean
Ireland's Central Statistics Office counts Seรกn and Sean as two different names. In the 2024 birth registrations Seรกn, with the sรญneadh fada, ranked 15th among boys' names; Sean without it ranked 123rd. The CSO says both spellings “are treated as two separate names since 2018”. Before that they were merged. The office has published babies' forenames since 1998, and a decision taken that year was to input names without sรญnte fada; changing it later would have broken the series. Feedback after the 2017 launch of its baby names app is what moved it.
The accent reached the statute book too. Section 9A of the Official Languages Act 2003, inserted by the Official Languages (Amendment) Act 2021, requires prescribed public bodies to run systems that let a person's name in Irish — including its patronymic or matronymic form — be recorded correctly, and that facilitate the use of the length accent. Rarity is a counting question, and here the spelling is the count.
๐๏ธ Eye Color
| Blue | 55% |
| Green | 15% |
| Gray | 8% |
| Hazel | 12% |
| Brown | 10% |
๐ Hair Color
| Brown | 30% |
| Dark Brown | 20% |
| Red | 10% |
| Blonde | 18% |
| Black | 12% |
| Gray | 10% |
๐ฉธ Blood Type
| O+ | 47% |
| A+ | 26% |
| B+ | 8% |
| AB+ | 2% |
| O- | 8% |
| A- | 5% |
| B- | 2% |
| AB- | 2% |
Trait frequencies on this page come from public and institutional datasets โ see Data Sources.
🧮 Calculate Your Rarity in Ireland
Pick your eye colour, hair colour and blood type. The calculator uses Ireland's own figures from the tables above, not world averages.
This is an estimate, not a measurement. It multiplies three national frequencies as if they were independent, and they are not: eye and hair colour share pigmentation genes, so a combination that tends to run together, such as blue eyes with blonde hair, is more common than the multiplication suggests, while one that rarely does, such as blue eyes with black hair, is rarer. Blood type is independent of both. The frequencies are national averages from public datasets — see Data Sources.
That number describes the body you were born with. Fraeon, our other site, does the same arithmetic for the part you chose: the films, series, games, books, anime and manga you have actually finished. Start your log →
๐๏ธ Why Almost No 19th-Century Irish Census Survives
Almost no nineteenth-century Irish census survives, and the famous fire is only part of it. The National Archives of Ireland says the majority of returns for 1821, 1831, 1841 and 1851 were destroyed in a fire during the Irish Civil War in 1922. No individual household returns exist for 1861, 1871, 1881 or 1891 either, and those losses were decisions rather than accidents: the 1861 and 1871 returns were “deliberately destroyed in 1877 after analysis was complete”, and the 1881 and 1891 returns “were destroyed during the First World War, due to a paper shortage”.
The 1922 loss is being partly undone. Trinity College Dublin dates the destruction of the Public Record Office's Record Treasury to 30 June 1922; the Virtual Record Treasury of Ireland, led by Trinity with the SFI ADAPT Centre, now holds 150,000 records, 50 million words of text and more than 6,000 maps covering 1174 to 1922, rebuilt from 70 institutions worldwide.
๐ฉธ O in the West, Rhesus Negative in the East
The blood table above is a national average, and the Irish Blood Transfusion Service — the national blood service — says the country underneath it is not uniform. It states that people in the West of Ireland are predominantly of blood group O, that there are more people with Rhesus negative blood on the East coast than the West, and that there is a higher concentration of Group A blood in counties which historically received Viking, Anglo Norman and English population settlements. The link to settlement history is the service's, not ours.
So a single national figure flattens that variation, and where in Ireland you are moves it. The IBTS also puts O positive at 47% of the population and AB negative at 1% — worth noting, because the table above says 2% for AB negative. More on groups at rarest blood type.
โญ Rare Facts About Ireland
Where these numbers come from
The name figures are from the Central Statistics Office; the nineteenth-century census history is from the National Archives of Ireland. The Irish Blood Transfusion Service publishes its own figures for Ireland, and where the blood table above differs from them, the note below says so. The eye colour, hair colour and height figures have no official Irish source at all: they are estimates from compiled datasets, not an official count. Last checked: September 2026.