The majority of the Irish in America before the nineteenth century were those who later became known as Scotch-Irish, descendants of people from Scotland who had moved to the northern part of Ireland in earlier centuries. These northern Irish were mainly Protestant, and distinctions between the them and other Irish immigrants came into popular usage in the nineteenth century when much larger numbers of Roman Catholic Irish began to arrive. Northern Irish migration peaked between the 1750’s and the early 1770’s, with an estimated 14,200 people from Northern Ireland reaching America during the 1750’s, 21,200 during the 1760’s, and 13,200 during the first of the 1770’s, leading up to the American Revolution. Most of the pre-Revolutionary War immigration from Ireland took place between 1760 and 1775, when about 25,000 new arrivals came to the colonies.
The first U.S. Census in 1790 may have underestimated the proportion of the population that was of Irish background. However, in 1931 scholars who studied the linguistic and national background origin of the American people at the time of that first U.S. Census estimated that about one out of every ten Americans in 1790 was of Irish ancestry, including both Protestants and a smaller numbers of Catholics. The 1931 estimates indicated that people of Irish ancestry could be found in all parts of the new nation, but that they made up the largest proportions of populations in the South. According to these figures, in 1790, people of Irish background made up 15 percent of residents in Georgia, 14 percent in South Carolina, 12 percent in Kentucky and Tennessee, and 11 percent in Virginia and North Carolina. As immigration from Ireland and other parts of Europe increased during the first half of the nineteenth century, however, the new immigrants tended to settle in the North and in the most urbanized parts of the country, rather than in the rural South.