Emigration
While the famine was responsible for a significant increase in emigration from Ireland, of anywhere from 45% to nearly 85% depending on the year and the county, it was not the sole cause. Nor was it even the era when mass emigration from Ireland commenced. That can be traced to the middle of the 18th century, when some 250,000 people left Ireland to settle in the New World alone, over a period of some 50 years. From the defeat of Napoleon to the beginning of the famine, a period of 30 years, "at least 1,000,000 and possibly 1,500,000 emigrated". However, during the worst of the famine, emigration reached somewhere around 250,000 in one year alone, with far more emigrants leaving from western Ireland than any other part.
Families did not migrate en masse but younger members of families did. So much so that emigration almost became a rite of passage, as evidenced by the data that show that, unlike similar emigration throughout world history, women emigrated just as often, just as early, and in the same numbers as men. The emigrant started a new life in a new land, sent remittances " £1,404,000 by 1851" back to his/her family in Ireland which, in turn, allowed another member of the family to emigrate.
Emigration during the famine years of 1845–1850 was to England, Scotland, the U.S., Canada, and Australia. Many of those fleeing to the Americas used the well-established McCorkell Line.
Of the 100,000 Irish that sailed to Canada in 1847, an estimated one out of five died from disease and malnutrition, including over 5,000 at Grosse Isle. Mortality rates of 30% aboard the coffin ships were common.
By 1854, between 1.5 and 2 million Irish left their country due to evictions, starvation, and harsh living conditions. In America, most Irish became city-dwellers: with little money, many had to settle in the cities that the ships they came on landed in. By 1850, the Irish made up a quarter of the population in Boston, Massachusetts; New York City; Philadelphia, Pennsylvania; and Baltimore, Maryland. In addition, Irish populations became prevalent in some American mining communities.
The 1851 census reported that more than half the inhabitants of Toronto, Ontario were Irish, and in 1847 alone, 38,000 famine Irish flooded a city with fewer than 20,000 citizens. Other Canadian cities such as Saint John, New Brunswick; Quebec City and Montreal, Quebec; Ottawa, Kingston and Hamilton, Ontario also received large numbers of Famine Irish since Canada, as part of the British Empire, could not close its ports to Irish ships (unlike the U.S.), and they could get passage cheaply (or free in the case of tenant evictions) in returning empty lumber holds. However fearing nationalist insurgencies the British government placed harsh restrictions on Irish immigration to Canada after 1847 resulting in larger influxes to the U.S. The largest Famine grave site outside of Ireland is at Grosse-Île, Quebec, an island in the St. Lawrence River used to quarantine ships near Quebec City. In 1851, about a quarter of Liverpool's population was Irish-born.
The famine marked the beginning of the steep depopulation of Ireland in the 19th century. Population had increased by 13–14% in the first three decades of the 19th century. Between 1831 and 1841, population grew by 5%. Application of Thomas Malthus's idea of population expanding geometrically while resources increase arithmetically was popular during the famines of 1817 and 1822. However by the 1830s, a decade before the famine, they were seen as overly simplistic and Ireland's problems were seen "less as an excess of population than as a lack of capital investment." The population of Ireland was increasing no faster than that of England, which suffered no equivalent catastrophe.
Read more about this topic: Great Famine (Ireland)