County Armagh is one of the six counties of Northern Ireland, though these are no longer units of local government, and County Armagh is divided between two council districts. It has a long border with the Republic of Ireland, which made it a dangerous place during the Troubles of the late 20th century. All that is in the past, and nowadays you visit for its ecclesiastic and prehistoric sights and attractive countryside.
The county is named for its city of Armagh, which derives from the Irish Ard Macha - the heights of Macha. "Magh" also indicates a plain, a common place-name element, and Macha was a fertile goddess of the plains. She had multiple guises and in one legend, the men of Ulster forced her to run a race against horses while she was heavily pregnant. She won, giving birth to twins on the finish line, and cursed those men to suffer weakness whenever they were most vulnerable, such as in battle. The curse lasted for nine generations so it's long ago expired.
The area has held great religious significance since prehistoric times, as shown by the complex at Navan Fort west of Armagh. It was a Neolithic dwelling place but the "roundhouse" is a religious structure from 95 BC. St Patrick founded a church there in 455 AD and declared Armagh to be the ecclesiastic capital of Ireland, and so it has remained for both Roman Catholics and Protestants. The area was traditionally part of the province of Ulster, which was divided into shires - counties - at the end of the Nine Years' War in 1603. North and central County Armagh has the best farmland, with low, slightly rolling countryside and many orchards. This part became settled by Plantations - planned townships of loyal Protestants, many from Scotland, to prevent further Irish rebellion against English rule. Industry developed from the 18th century as the linen trade grew, and there was better transport to Belfast. The south of the county is hilly, with glacial drumlins, rising to Slieve Gullion and the Cooley mountains. This land is less productive and retained a Catholic majority population, creating a social fault line which cracked open during the late-20th-century "Troubles".
In 1921 Ireland was partitioned, with a provisional border based on the counties, and County Armagh was one of the six that joined Northern Ireland, a constituent part of the United Kingdom just like Wales and Scotland. Southern Ireland, with the other 26 counties, nominally also remained in the UK, but London and Dublin somehow weren't on the same page and it moved towards independence. A boundary commission was set up, which recommended transferring south Armagh to Southern Ireland; but it was politically sabotaged, its report was suppressed until 1969, and no changes were made.
"The Troubles", the sectarian division (exacerbated by economic decline) that poisoned Ulster, began in 1969 and continued for 30 years. The position of the border was never a major issue, it was the legitimacy of that border and continuation of a British-ruled part of Ireland that was the basis of conflict, along with other grievances. Still, it did not sweeten local opinion to learn that they might have belonged to the Republic all along. South Armagh became a badlands of smuggling and banditry, with a heavy army presence, a place of concrete lookout turrets and checkpoints and low-flying helicopters. At least 58 police officers and 124 soldiers were killed by the "Provos" — the Provisional Irish Republican Army — in this area, many near the border village of Crossmaglen.
The Good Friday Agreement of 1998 enshrined non-violence and mutual respect of national borders, and has led to peace; it helped that both UK and Ireland were part of the European Union, fostering economic ties. This peace has enabled Belfast and Derry to regenerate and become mainstream tourist destinations; other areas including County Armagh saw less benefit. In 2011 the counties of Northern Ireland were abolished, and local government was divided into 26 districts that were obviously too small. In 2015 they were re-organised into 11 "super-districts". An area roughly corresponding to the north and central county is now the Armagh, Banbridge and Craigavon District, while the south is in Newry, Mourne and Down District.
See Northern Ireland#Get in for routes by air and sea. County Armagh is within a couple of hours drive from any port of entry.
Trains run every 30 min from Bangor via Belfast to Lurgan and Portadown. The Dublin-Belfast Enterprise Train runs eight times a day (5 on Sunday) stopping at Newry and Portadown.
Bus 251 runs hourly from Belfast to Portadown and Armagh, and some continue across the border to Monaghan and Cavan. Bus X4 from Dublin Busáras and Airport runs daily to Armagh and continues to Dungannon, Cookstown and Derry.
By car from Belfast follow M1 west to Lurgan, then A3 through Portadown to Armagh. From Dublin leave M1 / N1 / A1 at Newry and follow A28 towards Armagh. Your main task is to avoid rush hour.
You can get between the towns by bus, but many of the sights are out in the countryside, with little or no public transport. A bike would do, but a car gives you shelter from the rain.
A network of national cycleways crosses the county, though they're mostly on road.
Standard advice about road safety, protecting valuables, and suitable clothing if you climb the hills.
The border area is nowadays safe; just remember that many people here lost family members in the Troubles so there's still a raw nerve.
Primary administrative division