Seventeenth century Ireland witnessed very significant levels of population turnover and migration. Approximately 260,000 British settlers came to Ireland during the course of the century whilst an estimated 130,000 Irish emigrated over the same period. The significance of these migration flows is enhanced if we consider them in a relative rather than absolute way. The contemporary emigrant flow for the century is less than the numbers who left during certain single years in the later 1840s. Given that Ireland’s estimated population in 1641 was only 2.1 million, however, we can deduce that the emigration rate constituted about 6.2% of mid-century population. The dominant destination throughout the century for Irish migrants was continental Europe which absorbed some 90,000 migrants. Of these the majority were military migrants leaving Ireland in particular volume after the military reverses of 1601, the early 1650s and 1691. The Americas, particularly the British Caribbean, became a significant destination during the second half of the century, receiving an estimated 30,000 migrants. Britain during the course of the century received Irish migrants and returning settlers who may have constituted as a whole, a movement of about 10,000 souls.

Eighteenth-century Ireland witnessed a significant increase in the volume of emigration in both absolute and proportional terms. With a reduction in significant immigration after 1700 and weak demographic expansion during the first half of the century, the country’s population had only grown to around 2.4 million by the early 1750s. Thus with the emigration of an estimated 265,000 over the course of the century we can deduce an emigration rate of 11%. Historians hotly contend the volume of migration to North America, the dominant destination. Most recent estimates suggest something in the region of 110,000 emigrants crossed the Atlantic from Ireland in the decades before the American Revolution. If we allow for the migration of a further 40,000 emigrants between 1782 and 1800 that would provide a total of 150,000 emigrants to North America for the century as a whole. It is thought that about 60% of these emigrants were drawn from the northern province of Ulster and that at least two-thirds were Presbyterians of Scottish ancestry. Migration to Europe, particularly during the first half of the century and particularly by Irish Catholics from the south-east of the country, remained significant. Opportunities for military service, education and trade drew an estimated 60,000 to the continent. The flow east towards Britain is poorly recorded and difficult to estimate. One might suggest a total in the region of 50,000. Finally, the beginnings of convict transportation to Australia during the 1790s saw no more than 5000 Irish migrate to the Antipodes.

The nineteenth century was without doubt the most significant century in terms of establishing the Irish diaspora. The dominance of North America as the favoured destination for Irish migrants was enhanced with a staggering 5 million emigrants crossing the Atlantic between 1800 and 1900. British North America, what would later become Canada, was a significant place of settlement in the first half of the century with 2 out of every 5 Irish trans-Atlantic emigrants in the pre-Famine era settling north of the 49th parallel. This represents a total of about 400,000 emigrants. Britain, by some distance was the second most important destination for nineteenth century emigrants. Estimating the volume of this flow is severely hampered by the absence of any systematic recording of movement across the Irish Sea. The fact that many migrants spent time in Britain prior to departure for New World destinations or moved on a seasonal basis adds to the statistical conundrum. Nonetheless, throughout the course of the nineteenth century it is probable that somewhere in the region of 1.5 million migrants crossed from Ireland to Britain. Britain’s colonies also absorbed a smaller proportion of Irish emigrants. Over the course of the century Australia received an estimated 350,000 Irish, New Zealand about 80,000 and South Africa no more than 15,000. Argentina, which in terms of mercantile trade could be thought of as a quasi-British colony, acted as a destination about 30,000 Irish emigrants. The massive scale of Irish emigration between these dates becomes clearer when, on the basis of an 1841 population of 8,175,124 and a total of 6,975,000 emigrants, we calculate an emigration rate of 85.3%. Two interesting features of this exodus become apparent when set into the wider European context. In Ireland the gender profile of emigration was more evenly balanced than was the case in most other European countries, where male departures predominated. It was also the case that a relatively small proportion of the emigrants who left Ireland for New World destinations returned (approximately 1 in 10) as compared to a European average of about 3 in 10.

Although the relative scale of emigration declined from its mid-nineteenth century heights Irish emigration by contemporary European standards remained prolific throughout much of the twentieth century. The partition of the island from 1921 makes the compilation of statistics even more problematic. The peaks in emigration from the southern state during the 1930s, between 1945 and 1955 and again in the late 1980s, may not have been matched by movement out of Northern Ireland. The lack of exploration of the latter phenomenon, however, should not be taken as an indication of limited emigration. One profound shift which occurred during the later 1920s was the replacement of North America by Britain as the dominant migrant destination. Proposing an estimate for the total migration flow from all 32 counties of Ireland across the Irish Sea over the course of the century is a precarious enterprise, even the acknowledged expert in this field refuses to offer a number. It may be tentatively proposed that somewhere in the region of 1.2 million emigrants followed this course. Emigration to the whole of North America from Ireland north and south probably totalled about 1.1 million with more than two-thirds of these emigrants departing before 1930. Other overseas destinations probably accounted for a further 150,000 Irish emigrants with continental Europe re-emerging somewhat following the Republic of Ireland’s entry of the EEC in 1973. Based on a population for the island of Ireland in 1951 of 4,331,514 the emigration rate for the twentieth century works out at 56.5%.