How we work

Methodology & sources

Name: Irish surname statistics from the 1901, 1911 and 1926 censuses
Creator: surnames.ie

Every number on surnames.ie comes from a census return, and every statement about meaning or history has a footnote. This page explains how.

The census figures

Counts come from the complete transcribed returns of the censuses of Ireland taken in 1901 and 1911, and the 1926 census of the Irish Free State, released by the National Archives of Ireland. Together they hold 11,781,090 person entries. We compile them from the same database that powers irishcensus.com.

Counts are census entries, not unique people. Someone alive in 1901 and 1911 is counted in both years.
1926 covers 26 counties. Northern Ireland was not part of the 1926 Free State census, so 1926 shares and ranks use a smaller population.
Spellings are combined where they are the same name: Sullivan and O'Sullivan, Byrne and O'Byrne, Smith and Smyth, Maguire and McGuire, Sweeney and McSweeney. We do not merge Mac and O' forms that belong to unrelated families: McDonnell is not O'Donnell, and McNeill is not O'Neill.
County rankings count the people living in each county on census night, across every surname in the census, merged the same way. Names without a page here have their O' and plain forms combined, and nothing else.
Rates per 10,000 divide the number of bearers in a county by that county's census population in the same year. A concentration index of 2 means the name was twice as common there as across Ireland.
Local strongholds are District Electoral Divisions with at least 300 residents, ranked by the share of residents bearing the name.
Religion, Irish language and literacy are grouped from the free-text answers on the forms. In 1901 and 1911 a blank language entry meant English only. Literacy is measured among people aged 15 and over. The 1926 transcription has no literacy or occupation data.
Fertility uses the 1911 question on children born alive to each married woman. We report women aged 45–59, whose families were largely complete.
Occupations are the most frequent wordings, tidied for capitalisation but otherwise as written.

Meanings, Irish forms and history

Editorial text is written fresh for surnames.ie from the sources below and footnoted on every page. We paraphrase rather than copy, and we leave a claim out rather than guess.

Patrick Woulfe, Sloinnte Gaedheal is Gall (1923). The standard early dictionary of Irish surnames, used for Irish forms, meanings and sept seats.
Gaois surname database (Fiontar & Scoil na Gaeilge, Dublin City University), used for modern standard Irish forms.
Dictionary of Irish Biography and Wikipedia, used for historical figures and dynasties. These are cross-checked and paraphrased.
Burke's General Armory (1884) and O'Hart's Irish Pedigrees (1892), used for heraldry and pedigrees, each attributed to the source that makes the claim.
US Census Bureau 2010 surname file, used for the American figures.

We do not use commercial crest or “family history” sites as sources.

Coats of arms

There is no such thing as a coat of arms for a surname. Arms were granted or confirmed to individuals and passed to their descendants. Where a source records arms for a particular family, we say whose they were.

Maps

County outlines are derived from Ordnance Survey Ireland (CC BY 4.0) and OSNI (Open Government Licence) open data. They are modern boundaries, close to but not identical with the census-era counties.

Corrections

If you spot an error, tell us via the contact page, with the page and your source. We correct mistakes and note significant changes.