Many of the early European settlers of Appalachia, an area that includes the places you’ve named, were from Ireland, but are what came later to be called Scots Irish or Ulster Scots, after the part of Ireland they had come from, Ulster, an area of six counties in the north and northeast of the island of Ireland.
Due to a complex of socio-historical factors, the British crown wanted to have full control over Ireland, including their economy, their political affairs, and their religion. As you have pointed out, many Irish people are Roman Catholic. You may recall that after the Protestant reformation, the English eventually landed in a camp firmly opposed to Roman Catholicism. However, they were also firmly opposed to more Protestant forms of church governance, including Presbyterianism, which many Scots and people living on the borderland between Scotland and England were adhering to by the early 1600s.
By the mid 1600, there was unrest and political turmoil owing to a poor harvest and Irish Catholics being fed up at their second class treatment. After some rebellions in the 1640s and Oliver Cromwell’s rise to power, an even bloodier chapter was ushered in. In the 1680s and 90s, yet more Scots were driven to Ulster by famine in their homeland, and by the end of the 17th century, Presbyterianism became the majority religion in NI.
By 1700, colonization of British North America was in full swing; seeking more land and a further removal from the meddlesome influence of the British government, Scots Irish populations began settling the Americas, largely concentrating in Pennsylvania during the first waves of immigration, and filtering further south and west into and across the mountains as those areas opened up for Anglo settlement as the 18th wore on. For a salient illustration of these migration patterns, check out this map of Northern Irish place names found in the US, and note how neatly it correlates with the Appalachian region. Or, for a more highly specific but more academic exploration of the topic, here is a dive into Ulster place names in Pennsylvania and their histories.
Hence, while being very similar in many ways to the majority of Irish people, the Scots Irish do differ from that population in several salient ways, some of which—including religious demographics—endure to the present day, both in Britain/Ireland as well as the US.
That’s because Scots-Irish is a bit of a misnomer. To understand who these people settling the Appalachian Back Country really were, we need to fast forward back to the early 1600s.
In 1603, Queen Elizabeth I died and her cousin, James VI of Scotland, succeeded her as King of England and Ireland. Elizabeth had had serious problems in asserting her authority in Ireland. The break with Rome under her father, Henry VIII, had not been well-received there at all, and her brother, Edward VI, hadn’t sent enough Gaelic-speaking Protestant preachers to convince the Irish peasantry that this new religion was a good idea. Elizabeth I faced many Catholic rebellions in Ireland, which had the backing of the Spanish Empire and the Papacy. The worst of these was the Nine Years War of May 1593 to 30 March 1603, which tied down more English troops overseas (about 18,000 armed men) than any conflict had done since the Hundred Years’ War. The epicentre of that rebellion had been in Ulster in the north east, and it’s ringleader was Hugh O’Neill, Earl of Tyrone. While the rebellion was thoroughly defeated and Hugh O’Neill and the other Catholic rebel earls were forced into exile in Continental Europe, it very nearly reversed seventy years of English territorial gains in Ireland - back in 1533, all the English effectively controlled was a “Pale of Settlement” around Dublin and Waterford on the east coast. Indeed it’s from that we get the phrase “beyond the pale”, meaning something barbaric.
King James needed to make sure that his third kingdom (Ireland) would not flare up in rebellion again. And he had other domestic problems to deal with. The Union of crowns in 1603 meant that the Anglo-Scottish border no longer needed to be militarised. But a long period of on and off warfare between England and Scotland from 1296 to 1560 had meant that society in the regions on either side of the border had basically become organised for war. The aristocracy in the Northern English counties of Cumberland, Westmorland and Northumberland and on the Scottish side of the border as well possessed private armies numbering in the hundreds and even low thousands in some cases, had a strong clannish mentality and observed very strict, touchy codes of honour - showing your back to a rival lord was seen as an insult that could merit vengeance. Even when England and Scotland were at peace, they still feuded with each other, raiding each other’s cattle farms, burning each other’s homes, holding rival clan members to ransom, causing massive public order problems that required cross border co-operation between Elizabeth I and James in order to solve. The peasantry in these regions were much rougher and more militarised than elsewhere - society for them revolved not around the manor, the village and the parish church, but around much more scattered and temporary homesteads (log cabins were a thing there) and around performing military service to their lords. Every free farmer was expected to own a “steel bonnet” (an open-faced helmet), a breastplate, knee-length boots, a lance, a dagger, two pistols and a swift pony. These were the “border reivers”, and one could say they were like the mafia of their day. Indeed, they even invented the word “blackmail”, based on the rituals the lord of a border revived clan would perform when threatening a raid on a rival.
Most of the border reivers in Scotland followed the Presbyterian form of Protestant Christianity that had spread like wildfire around Scotland during James I’s childhood when the Scottish Reformation was taking place. James I, however, preferred a more episcopalian form of Christianity, like the Church of England, because it would afford him greater control over the Scottish church. Unlike his son Charles I would do, to disastrous effect, in the 1630s, he didn’t meddle too much with the religious status quo in Scotland. But he did try and get as many of the Presbyterians of the less domesticated diet, less amenable to his royal authority in religious matters, outside of the kingdom.
Thus to kill many birds with one stone, the English built plantations in Northern Ireland, especially in Ulster, and invited settlers from the Anglo-Scottish borders to come there. Their traditions of frontier warfare made them perfect for it, combined with their militant Protestantism.
Fast forward to the eighteenth century, these ex-border reivers in Northern England and Southern Scotland still hadn’t forgotten their warrior traditions and resented the religious status quo and the increasingly meddlesome power of the British state. So they were invited to settle in the Back Country, to act as a bulwark against the French and Native Americans to the West. Many of their old border-reiver traditions, including feuding, survived well-into the 1800s I.e. the infamous Hatfield-McCoy feud, and today these regions still strongly resent “big government.” Many Americans today still hold the surnames of border reiver clans I.e. Nixon, Armstrong, Jackson, Elliot, Thompson, Simpson etc, especially those with connections to the former Back Country states. However, the border reiver roots became increasingly forgotten and so by the 1800s, they were already being known by the misnomer of “Scots-Irish
