Ireland

Ireland, officially the Republic of Ireland, was a country located in Europe before the Great War.

Background
In the Commonwealth, there is an abundance of Irish republican flags, indicating that Ireland was its own independent nation before the Great War. There are other references to Celts and characters with Irish surnames throughout the Fallout series, though it is not confirmed if they refer to the Republic of Ireland or Northern Ireland, which is part of the United Kingdom.

Fallout

 * Patrick the Celt is descended from Americanized Celts and keeps his heritage alive by collecting clothing, food, stories, songs and knowledge of Celtic history. He knows the Irish song "Na Gheala Mbeadh" which is very poor Irish for "The Light Would," possibly a mistranslation of "Mo Ghile Mear," or "My Gallant Darling."

Fallout 2

 * John L. Sullivan references Irish folklore, has a distinctly Irish accent and uses the phrase "Erin go bragh!" This is an English corruption of the phrase "Éirinn go Brách," which means "Ireland forever."
 * John Cassidy's last name is of Irish origin. John's father named him after a pre-War comic book character.
 * In Fallout 2, Arch Dornan, despite being of American nationality, has a relatively obscure Irish surname.
 * Frank Horrigan, the main antagonist and final boss of Fallout 2, has a surname of Irish origin.

Fallout 3

 * In the quest Stealing Independence, Abraham Washington will erroneously refer to Fort McHenry as "Fort McHarry." James McHenry was an Irish-born military surgeon and an important figure in the American Revolutionary War.
 * Colin Moriarty speaks with a working class Dublin accent. He claims he has lived in the United States for most of his life, but does not specifically state where he came from.
 * The armor worn by Reilly's Rangers includes a four-leaf clover on it, a symbol typically associated with Irish-Americans.

Fallout: New Vegas

 * In multiple places in the Mojave Wasteland and the Divide, graffiti can be found which states "the centre cannot hold," a quote from the Irish poet W. B. Yeats' poem "The Second Coming."
 * Caleb McCaffery's last name is of Irish origin.
 * Nolan McNamara's first and last names are of Irish origin.
 * Elizabeth Kieran surname is of Irish origin.
 * Dusty McBride surname is of Irish origin.
 * Rose of Sharon Cassidy surname is of Irish origin.
 * Liza O'Malley A receptionist for the NCR Embassy last name is of Irish origin.
 * Dermot A slaver living in Westside name is of Irish origin, in the Irish language Dermot means Without envy
 * Hannigan a member of the powdergangers name is of Irish origin.
 * Lt. Haggerty surname is of Irish origin.
 * Chief Hanlon Surname is of Irish origin.
 * Private O'Hanrahan last name is Irish.
 * Arcade Gannon last name is of Irish origin anglicized from Irish Mag Fhionnáin meaning white.

Fallout 4
Because fallout 4 takes place in Boston a area of the united states which historically had huge Irish immigration many characters in fallout 4 have Irish first and last names.
 * Cait speaks with a working class Dublin accent.
 * Irish Pride Industries shipyard contains many references to Irish-American culture, which itself comes from Irish immigration to the United States.
 * The Eddie Winter holotapes reference Irish gangs operating in the Boston area, as well as a trip to Ireland in holotape 9.
 * The Four Leaf Clover perk icon and Shamrock Taphouse logo contain the national flag of Ireland.
 * Whiskey bottles in Fallout 4 are marked as Irish whiskey and have the word "whiskey" written in the Irish language.
 * John Hancock's real name is John McDonough, a surname that is of Irish origin. Mayor McDonough of Diamond City is his brother.
 * Mama Murphy's last name is of Irish origin.
 * Kent Connolly surname is of Irish origin.
 * Becky Fallon last name is Irish.
 * Edward Deegan surname is of Irish origin.
 * Shaun the sole survivors son has a first name of Irish origin from Irish Séan.
 * Lancer Captain Kells last name is of Irish origin named after Kells, a town in County Meath, Ireland.
 * General McGann last leader of the minute men surname is of Irish origin.
 * Talia McGovern surname is of Irish origin.
 * Penny Fitzgerald last name is of Irish-Norman origin.
 * Parker Quinn last name is of Irish origin.
 * Patrick A very typical Irish name long associated with Ireland for over a millennia.
 * Danny Sullivan A gate guard of diamond city last name is of Irish origin.
 * In a recording made by Rebecca Lineholm and Gemma, the latter says, "Oh, Rebecca! That's very rebellious of you. Drinking in Paul Revere's house. I'll get my coat and a bottle of Irish!"
 * Like the one in Fallout 3, the Luck bobblehead in Fallout 4 has a four-leaf clover and an Irish buckle hat, a reference to the saying, "luck of the Irish."
 * Old Longfellow sings traditional Irish songs while idle.

Fallout 76

 * Ogham, an Early Medieval alphabet used to write the primitive Irish language that originated in Ireland, is mentioned in the Vault-Tec University terminal entries.
 * Kesha McDermott's last name is of Irish origin.
 * Visce Beatha is a pre-war whiskey label that was based in Ireland. the word Visce Beatha is a corruption of Uisce beatha, which is where the word whiskey comes from in English.
 * Skis found in Appalachia are the Ski-O-Matic brand, with a clover logo.

Fallout Tactics

 * A Brotherhood of Steel paladin guarding a bunker is named McCarthy, which is of Irish origin.

Known locations

 * Dublin (mentioned in Fallout 4)
 * Galway Bay (mentioned in Fallout 4)
 * Kilkenny (mentioned in Fallout 4)
 * Waterford (mentioned in Fallout 4)