For centuries, even though the Norman invasion of the English, Irish last names were defined by clans and septs (smaller groups within clans). During the British colonization of Ireland, last names were changed to sound more Anglican. Because of this disruption to Gaelic life, research into Irish genealogy is challenging because of the changing and disappearance of some names over time.

Many Irish surnames we are familiar with that begin with Mc or Mac are patronyms; Mc and Mac stand for “son,” so Mc Doyle would mean Son of Doyle. The familiar O means “grandson," therefore O’Brien means Grandson of O’Brien. Irish last names are also often based on physical characteristics, clan names, and the region from which the family hailed. 

Patronymic Irish Surnames (and Meanings) 

Like many cultures, many Irish last names follow the patronymic tradition of a family name being based on the father’s or grandfather’s first name. In addition to Mc, Mac, and O, the commonly used Fitz is an influence of the French Fis, meaning son. 

1. Fitzgerald - Son of Gerald.
2. McCarthy  - Anglicized version of the Gaelic Mac Cárthaigh. 
3. O’Brien - Grandson of Brien or Brian. Brian Boru was the King of Ireland in the 10th century. The O’Brien or O’Briain is one of Ireland’s oldest aristocratic families. 
4. O’Connor - Grandson of Connor.
5. O’Kelly - Anglicized version of O'Ceallaigh.
6. O’Leary - Descendant of Laoghaire.
7. O’More - Scottish and Gaelic origins. Alternative spellings Moore, Muir, and Mure.
8. O’Murphy - Anglicized version O’Murchadha.
9. O’Neill - Grandson of Neil. Alternative spelling O’Niall.
10. O’Reilly - Grandson of Reilly.

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Irish Last Names Based on Region  (and Meanings) 

Irish last names can be widespread in one area and nearly non-existent in another. Here are some Irish last names specific to various regions of Ireland. 

1. Boyle - The last name Boyle is prevalent in Kildare and Offaly. The O’ Boyles were the chieftains of Donegal.
2. Byrne - Is common in Wicklow, Dublin, and Louth. An alternative spelling is Bran. It means raven.
3. Carroll - Carroll is a common last name in Ireland and quite popular in Armagh, Kerry, Louth, and Offaly.
4. Clarke - Clarke is one of the oldest surnames in Ireland. It is most prevalent in Cavan.
5. Deasun - Is a last name that refers to those from South Munster. 
6. Dunne - This is the most common last name Laois. An alternative spelling is Donne. 
7. Martin - This name is popular in both Ireland and England. It is mainly found in Tyrone, Galway, and Westmeath in Ireland.
8. Ryan - Ryan is the most common surname in Tipperary and Carlow. It is also fairly common in Limerick. The name means little king. 
9. Shea - The last name Shea or Shay is originally from Kerry. It means esteemed or majestic. 
10. Walsh - The last name Walsh is very common in Ireland, and it signifies the Welsh people who moved to Ireland during the Norman invasion. 

Irish Surnames Based on Personality or Physical Traits  (and Meanings) 

The Irish have always loved words and language, and Ireland is known as a land of poets and playwrights. As a land that loves wordplay, it makes sense that many common Irish surnames are descriptive monikers.

1. Campbell - A Scottish surname that means crooked mouth or wry mouth. 
2. Casey - Casey is an Old Irish word that means vigilant. 
3. Collins - Derived from a Gaelic word that means whelp or young dog. 
4. Duffy - Duffy comes from a Celtic word that means dark or swarthy.
5. Farrell - Valiant warrior or man of valor.
6. Flynn - Flynn is a Gaelic name that means scarlet or red. It is a variant of Flanagan.
7. Hogan  - Hogan is a variant of a Gaelic word that means young.
8. Kennedy - Perhaps one of America's most famous Irish names means armored head or misshapen head. 
9. Quinn - This name means chief. 
10. Regan - This name is derived from Riagan, which means impulsive. 

Irish Surnames Derived from Clans  (and Meanings) 

Ireland, like other Celtic cultures, revolved around clans. Clans consisted of smaller family units, and over time people took on the clan name as their surname. 

1. Bell - The Bells were a clan initially from the Borders.
2. Brennan - Brennan is one of the most common last names in Ireland. 
3. Connell - The O’Connel clans were originally from Connacht, Ulster, and Munster.
4. Connelly - The Connelly Irish Family was originally from Galway but eventually, most settled in Cork, Meath, and Monaghan.
5. Fitzpatrick - Son of Patrick. The name comes from the Mac Giolla Phadraig Clan. 
6. Gallagher - The Gallagher clan has been around since the 4th century and is from Donegal. 
7. Hayes - This old Irish word means fire. The Hayes clan originated in Cork.
8. O’Donnell - The O’Donnell clan was originally from Clare and Galway. 
9. O’Sullivan - Grandson of Sullivan. This clan was originally from the lords of Cahir. 
10. Murray - The surname Murray represents the relationship between Ireland and Scotland. The Murrays originated in Scotland. 

What Is a Very Irish Last Name?

Among common Irish last names, a very Irish surname is "Murphy". According to the Central Statistics Office, Murphy is consistently the most prominent surname across Ireland. Other very Irish last names include Lillis, Moore, Burns, O'Brien, Kennedy, and O'Reilly; additionally, names like Kenny or Kenney, which have been anglicized from the Gaelic ó Cionaoith and O Coinne family names, are also quite common. Moreover, Kelly, which comes from the Gaelic surname “O'Ceallaigh”, meaning warrior or fighter, is another popular Irish name.