The second largest pre-Revolutionary European immigrant group.

The total number of Scots-Irish immigrants to the American Colonies is estimated at between 250,000 and 400,000, making them the second largest European immigrant group prior to the American Revolution. Despite this they are virtually ignored by American history textbooks. This is one factor those with this ancestry are all too often unaware of it.

A source of confusion is the term "Scots-Irish" which was not in common use until the mid-19th century. It came into common usage only after 1840 to distinguish them from the indigenous Catholic Irish immigrants fleeing the Potato Famine. Previously they were referred to simply as "Irish". "Scotch-Irish" and "Scots-Irish" are interchangeable. British historians refer to them as "Ulster Scots".

The vast majority of emigrants from Ireland to America before 1840 were the Protestants whose ancestors had been Scottish Lowlanders, along with minorities of English Puritans and French Huguenots. The indigenous Catholic population infrequently intermarried with the Protestant incomers and rarely emigrated until the Potato Famine of the 1840s when approximately 2.5 million mostly Catholic Irish migrated to America.

Both the migration of Scots Lowlanders to Northern Ireland (approx. 1610 - 1700) and that of Ulster Scots to the American Colonies (1717 - 1775) had a variety of causes including high rents, poor harvest, drought, famine, trade restrictions, religious strife and warfare. Economic issues were to be the predominant reason for both migrations.

The numbers and proportions of those immigrants who were to become the Scots-Irish, where they emigrated from, and their status on arrival is disputed. There are not accurate records surviving from that era from which to derive hard data. Most arrived in five surges between 1717 to 1775. The last, from 1765 to 1775, is said to have constituted two-thirds of their number. One source has a considerable number immigrating directly from the Scottish Lowlands and northern shires of England. The Scots-Irish immigrants, seen as uncouth and combative by the established colonists, were only welcomed by Pennsylvania. The proportions of those arriving as indentured servants is also in question.  One sources suggests they were not seen as desirable servants, perceived as proud and ungovernable by potential employers.

Open land on the frontier - before the American Revolution the eastern slope of the Appalachian Mountains - was the primary attraction. Usually entering through Philadelphia and nearby ports, they followed the Philadelphia Wagon Road west and south, eventually as far as Georgia (see a map of their migration routes). These settlers provided a protective barrier between the established English and German settlements of the eastern seaboard and the often hostile native tribes to the west. Their temperament and experience in decades of warfare in Ulster served them well on the frontier, this combined with guerrilla tactics borrowed from the American Indians. The advent of the long rifle, initially the product of German immigrants in Lancaster, Pennsylvania, gave them the wherewithal to effectively hunt in the wilderness and defend themselves against hostile Native American tribes.

A mainstay of the Patriot Revolutionary forces rebelling against the British Crown, George Washington considered them indispensable. King George III was to characterize the American Revolution as "a Presbyterian War". Moving west of the Appalachians, national origin blurred as the Scots-Irish integrated with English, Highlanders, Germans and other Europeans.

Should you research Scots-Irish ancestors, keep in mind that approximately 20% of this immigrant group had English ancestry. English incomers to Ulster would have arrived primarily from the northern shires of Britain, an area that shared many of the economic hardships suffered by the Scottish Lowlanders. They also shared many surnames, so that alone won't be a determining factor as to whether your ancestors originated in the Scottish Lowlands or England. They developed cordial relations with the Ulster Scots even before migrating to the American Colonies.

Contemporary quotes about the Scots-Irish.

On the settling of Scots in Ulster.

... the settling of religion, the introducing (of) civility, order, and government amongst a barbarous and unsubdued people, ... acts of piety and glory, and worthy always of a Christian prince to endeavor.
(The Lowland Scots) ... of a middle temper between the English tender and the Irish rude breeding, and a great deal more like to adventure to plant Ulster than the English, it (Ulster) lying far both from the English native land and, more from their humour, while it (Ulster) lies nigh to Scotland, and the inhabitants not far from their ancient Scots manner.
Two quotes from a letter from James I to Lord Deputy of Ireland Sir Arthur Chichester on the settling of Lowland Scots in Ulster.

On emigration from Ulster to the American Colonies.

We have had three bad harvest together... Above 4,200 men, women and children have been shipped off from home... above 3,100 this last summer... the humor has spread like a contagion distemper, and the people will hardly hear anybody that tries to cure them of their madness. The worse is, that it only effects Protestants, and reigns chiefly in the North, which is the seat of our linen manufacturer.
From a letter of Hugh Boulter, lord primate of Ireland, 1728.

On the motives for migration south from Pennsylvania.

The number of white people in Virginia is... growing every day more numerous by the migration of Irish who, not succeeding so well in Pennsylvania as the more frugal and industrious Germans, sell their lands in that province and to the latter, and take up new ground in the remote counties of Virginia, Maryland and South Carolina... These are chiefly Presbyterians from the northern part of Ireland, who in American are generally called Scotch-Irish.
From Account of the European Settlements in America by Edmund Burke, 1757.

On the Scots-Irish resistance to the Crown prior to the Revolution.

Not less than 20 itinerant Presbyterian, Baptist and Independent Preachers are maintain'd by the synods of Pennsylvania and New England to traverse this Country Poisoning the Minds of the People - Instilling democratic and Commonwealth Principles into their minds - Embittering them against the very name of Bishops , and Episcopal Government and laying deep their fatal Republican Notions and Principles, Especially That they owe no Subjection to Great Britain, That they are a Free People - that they are to pay allegiance to King George as their Sovereign - But as to Great Britain or the Parliament, or any there, that they have no more to think of nor about them than the Turk or Pope - Thus do these Itinerant Preachers sent from the Norther Colonies to pervert the Minds of the Vulgar.
Reverend Charles Woodmason, Church of England clergyman, in Carolina Piedmont, 1767.

On Scots-Irish Presbyterianism and the American Revolution.

There is no use crying about it. Cousin America has run off with a Presbyterian parson, and that is the end of it.
Horace Walpole before Parliament.

On the character of the Scots-Irish.

I doubt not that those (Scotch-Irish) pioneers who came to the the South and gave all their strength and devotion to the fabrication of such civilization as we have were grim and determined and stiff-necked and opinionated and fearless people. It is probably easier to admire them than it would have been pleasant to live with them. I spent my earliest days amongst them and I have no doubt that their attributes had been transmitted almost unmodified to them by their ancestors for generation after generation. They were and they are undemonstrative, apparently without affection and superficially cold. But they generally have opinions, right or wrong, and they are altogether willing, if not anxious, to stand my their opinions to their last breaths. I scarcely think our government could have come into being without them.
Personal correspondence of J. K. Hall, describing in 1941 his Scotch-Irish ancestors in North Carolina.