The first significant wave of Irish American immigration came in the 1720s. This period saw the arrival of the Scots-Irish, a term used in North America (but not elsewhere) to denote those who came from Ireland but had Scottish Presbyterian roots.
Philadelphia was the most popular destination port for Scots-Irish immigrants to America, mainly because the linen trade routes were already well established. They then moved into the Appalachian regions, the Ohio Valley, New England, The Carolinas and Georgia.
Unlike the 19th century chapter of Irish American history, when Catholic Irish immigrants turned their back on the land, most Scots-Irish immigrants continued their farming traditions.
Despite the official line, small numbers of Catholics also arrived in this period. They sailed from the southern Irish ports of Cork and Kinsale and some settled communities in Virginia and Maryland.
There were peaks and troughs in numbers of immigrants during these years. The rate of emigration was high in the late 1720s, and low in the 1930s, before rising in the 1740s and continuing to grow until the 1760s when some 20,000 departed from Ulster ports alone. From 1770 to 1774 the human traffic peaked with the arrival of some 30,000 mostly Scots-Irish immigrants in America.
By 1790, America had a white population of 3,100,000. Nearly half a million (447,000) are estimated to have been of Irish stock (either Irish-born or of Irish ancestry). Of these, some two-thirds (about 300,000) are thought to have originated in the province of Ulster.