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.

Fallout 4

 * 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.
 * 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!"

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.

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)