Some of these are straight translations of the county's own name. Some are a war, a treaty or a grudge. And a few of the best known cannot be explained at all, which is said here rather than papered over.
A warning about the lists you will find elsewhere: they disagree with each other, and several of them give Tyrone the Oak Leaf County, which belongs to Derry. Tyrone is the Red Hand. Everything below is taken from one source for all thirty-two so the set is at least consistent with itself.
5 of the 32 have no settled origin, and they are marked. Tipperary is the surprise there: the Premier County is one of the best-known nicknames in the country and nobody can show where it came from.
For the nine glens that cut down to the sea along the north-east coast. It is one of the few nicknames that is simply a description of the ground.
GAA colours: Saffron, White
For its apple orchards, which are old: Armagh has grown apples for centuries, and the Bramley is the crop it is known for.
GAA colours: Tangerine, White
For Bréifne, the kingdom that covered Cavan and Leitrim under the O'Rourkes and O'Reillys. The county is younger than the kingdom it is named for.
GAA colours: Blue, White
A modern nickname and a complaint: Donegal is the county most often left off the map, cut off from the rest of the Republic by the border and a long way from anyone making decisions.
GAA colours: Gold, Green
For the Mourne Mountains in the south of the county, where Slieve Donard carries the highest known passage tomb in Ireland on its summit.
GAA colours: Red, Black
For Lough Erne, upper and lower, which take up so much of the county that Fermanagh is often said to be half water. Devenish Island and its round tower sit in the middle of it.
GAA colours: Green, White
Straight from the name: Doire is an oak grove, and the city is Doire Cholm Cille, Colmcille's oak wood. The oak leaf is on the county crest.
GAA colours: White, Red
For the drumlins, the low egg-shaped hills left by the ice that make the whole of south Ulster hard to cross and easy to hide in.
GAA colours: White, Blue
For the Red Hand of Ulster, the emblem of the O'Neills, whose seat at Dungannon was the capital of Gaelic Ulster until the Flight of the Earls in 1607. Popular lists often give Tyrone the Oak Leaf instead, which belongs to Derry.
GAA colours: White, Red
For Browneshill dolmen outside Carlow town, whose capstone weighs an estimated 150 tonnes and is believed to be the heaviest in Europe. How Neolithic farmers raised it is still an open question.
GAA colours: Red, Gold, Green
Dublin has no single settled nickname the way the others do, and none appears in the standard reference. The Dubs is what people say, and the Pale is what the county was for four centuries.
GAA colours: Sky blue, Navy
For the Curragh and the horse country around it: the racecourse, the studs, and the flat limestone grassland that feeds them.
GAA colours: White
For Kilkenny marble, a black carboniferous limestone that polishes like marble without being any. It is in the kerbstones, the shopfronts and the cathedral.
GAA colours: Black, Amber
For the O'Mores, lords of Laois, who fought the first plantation in Ireland for decades after their lands were confiscated in 1548 and the Fort of Leix was built where Portlaoise stands now.
GAA colours: Blue, White
No nickname appears in the standard reference. The Slashers is what is used, after Myles 'the Slasher' O'Reilly, who was killed at the bridge of Finnea in 1646.
GAA colours: Royal blue, Gold
Because it is the smallest of the thirty-two, at 826 square kilometres. Carlow is next and is seventy square kilometres bigger.
GAA colours: Red, White
For Tara, where the high kings were inaugurated, and because Meath was once a province in its own right: the fifth fifth, in the middle, with the seat of the kingship inside it.
GAA colours: Green, Gold
From the county motto, Esto Fidelis, be faithful. Which is a neat answer to a county that spent three centuries called King's County after Philip II of Spain, Mary I's husband.
GAA colours: Green, White, Gold
For Lough Ree, Ennell, Owel and Derravaragh, the last of which is where the Children of Lir were said to have spent the first three hundred years of their nine hundred as swans.
GAA colours: Maroon, White
For its farming, which was held up in the 19th century as the model the rest of the country should copy. The Yellowbellies is the older and more argued-over name.
GAA colours: Purple, Gold
For the gardens and the glens: Powerscourt, Mount Usher, and the wooded valleys running down from the mountains within an hour of Dublin.
GAA colours: Blue, Gold
Nobody has settled it. One account has a banner captured from the enemy at Ramillies in 1706 by the Clare Dragoons of the Irish Brigade; another has the banners carried for Daniel O'Connell when he won the Clare election of 1828 and forced Catholic Emancipation. Both are good stories and neither is proven.
GAA colours: Saffron, Blue
Cork backed Perkin Warbeck, the pretender to the English throne, in 1491, and the name stuck. It was taken up again, and meant differently, during the War of Independence.
GAA colours: Red, White
The county's Irish name is Ciarraí, the people of Ciar, and Ciar was a son of Fergus mac Róich and Medb of Connacht. It has since been claimed by the footballers.
GAA colours: Green, Gold
For the Treaty of Limerick, signed in 1691 to end the Williamite war, and broken so quickly that Limerick has been called the city of the violated treaty ever since. The stone it was supposedly signed on still stands by the river.
GAA colours: Green
The origin is not documented, which is unusual for a nickname this well known. It is variously put down to the richness of the Golden Vale, or to the Butlers, Earls of Ormond, whose seat was in the county. Neither can be shown.
GAA colours: Blue, Gold
For the Déisi, the people who held this country long before the county existed. Declan was their bishop, and his medieval Life has him converting them before Patrick.
GAA colours: White, Blue
For the fourteen merchant families who ran the city for centuries: Blake, Joyce, Lynch, Bodkin and the rest. The name was originally an insult from Cromwellian forces, and the families took it up as a badge.
GAA colours: Maroon, White
For the dog roses in the hedges, in the county with the smallest population.
GAA colours: Green, Gold
The name says it. Maigh Eo is the plain of the yew trees, and the nickname is a translation of the county's own name rather than anything added to it. The Maritime County is also used, for the Atlantic coast.
GAA colours: Green, Red
No nickname appears in the standard reference. The Rossies is what people say, and the Sheep Stealers is what their neighbours say.
GAA colours: Primrose, Royal blue (Black and green until 1935.)
For W. B. Yeats, who spent his childhood summers here and put the county into the poems: Innisfree on Lough Gill, the faeries at Glencar, and Ben Bulben, under which he asked to be buried, and where his remains were brought in 1948.
GAA colours: Black, White
The nicknames here are taken from the infobox of each county's Wikipedia article, or, where the infobox has none, Wikipedia's List of Irish county nicknames, because the popular lists disagree with each other and get things wrong. Where a nickname's origin is genuinely unknown, and a few of the best-known ones are, this says so rather than choosing the nicest story.
Under each county is every nickname in Wikipedia's list (93 in all), with the list's own explanation, shortened. Where it offers more than one story, or only a "possibly", the nickname is marked as disputed. Some are insults, and they are left in because they are on the record. The GAA colours come from the infobox of each county GAA article on Wikipedia; the swatches are that article's colours, not official specifications.
Each county's own page has the rest of it: who held the land in every age, the surnames that belong there, its towns and its castles. All thirty-two →