Settlers, soldiers and townsfolk from across the water, and the names they left behind.
The biggest name here is Welsh before it is anything else. Walsh (Breathnach, the Welshman) was given to the Welsh speakers who came over in and after the Norman invasion of 1169, many of whose leaders held lordships in south Wales; it is now the fourth most common surname in Ireland. Joyce, Keating, Taaffe, Wallace and Rice took the same road, and are marked here as Norman-Welsh: Welsh families in a Norman army.
The English names come in layers. The oldest are the Old English of the walled towns — Kilkenny, Limerick, Cork, south Wexford and the Pale around Dublin, where English was spoken when the rest of the island spoke Irish. Sherlock, Shortall, Stack, Furlong and Hore belong to that world, and most have been in Ireland since the Middle Ages. The plantations of the seventeenth century added another layer across Ulster and the midlands, and the Cromwellian settlement another after 1650.
Then there are the names that are not what they look like. Smith in Ireland is very often Mac Gabhann, the son of the smith, translated rather than imported. Vaughan can be a Welsh settler or the Gaelic Ó Mocháin. Forde covers three separate Gaelic septs and some English settlers besides. When an English word was available for an Irish name, clerks used it — so an English-looking surname is a question, not an answer, and the page for each name says which.
Sources: Wikipedia — Walsh (surname) ↗ · Wikipedia — Old English (Ireland) ↗ · Wikipedia — Norman invasion of Ireland ↗
Homelands are the historic heartland of the name, not where the family is now — people moved, and the Famine and the plantations moved them further.
It is the fourth most common surname in Ireland and has been here since the 1170s. Breathnach means the Welshman: it was given to the Welsh speakers who arrived with and after the Norman invasion.
Often, yes. Mac Gabhann, the son of the smith, was a widespread Gaelic name, especially in Cavan, and was simply translated into English as Smith. Many Irish Smiths are Gaelic Irish by descent.
The descendants of the Norman and English settlers of the twelfth and thirteenth centuries, concentrated in the Pale around Dublin and the walled towns of the south and east, where English was spoken. Catholic, and loyal to the Crown until the Reformation set them apart from it.
21: Aylward, Carew, Esmonde, Fleming, Forde, Furlong, Hore, Jenkins and more.
Most often Wexford (6), Kilkenny (4), Mayo (4), Waterford (3).