In 1821, Ireland's population was just over 6.8 million people. During this time, the entire island was a part of the United Kingdom of Great Britain and Ireland, after both islands were united by the Acts of Union in 1800. From the graph we can see that the population enjoyed steady growth between 1821 and 1841, and it rose by almost 1.4 million people in this time. However the Great Famine, which lasted from 1845 to 1849, had a devastating impact on the population, causing it to drop from 8.18 million in 1841 to 6.55 million in 1851.
The Great Hunger
The famine was caused by a Europe-wide potato blight that contributed to mass starvation and death throughout the continent, although it's impact on Ireland was much harsher than anywhere else. The potato blight affected Ireland so severely as the majority of potatoes in Ireland were of a single variety which allowed the disease to spread much faster than in other countries. As the potato blight spread, the population became increasingly dependent on dairy and grain products, however a lot of these resources were relocated by the British military to combat food shortages in Britain. Due to disproportional dependency on potatoes, and mismanagement by the British government, over one million people died and a further one million emigrated. The Great Famine lasted from just 1845 to 1849, but it's legacy caused almost a century of population decline, and to this day, the population of Ireland has never exceeded it's pre-famine levels.
Road to recovery
The population decline continued well into the twentieth century, during which time the Republic of Ireland achieved independence from the British Empire. After centuries of fighting and rebellion against British rule, Irish nationalists finally gained independence from Britain in 1921, although the six counties with the largest Protestant populations formed Northern Ireland, which is still a part of the United Kingdom today. In spite of the conflict that overshadowed Ireland for much of the twentieth century, which claimed the lives of thousands of people (particularly during the Northern Irish Troubles), and despite Ireland's high emigration rate, the population began growing again in the second half of the 1900s. The population was at it's lowest from 1926 to 1961, where it remained around 4.3 million, but in the following half-century the population grew by over two million people, reaching 6.4 million in 2011, although this number is still lower than in 1821.
Gender stats
The difference between the male and female populations throughout Ireland's recent history has also remained relatively low. The largest difference occurred in 1831, where there are 170,000 more women than men, although these figures do not include military personnel which would reduce the difference significantly. The gap then remains under 60,000 throughout the twentieth century.
Population of the island of Ireland from 1821 to 2011
(in millions)
*ROI:1936, NI: 1937
**NI: 2001, ROI: 2002
***Estimates
Please note the difference in intervals between certain years. Some data from the early 1900s came at irregular years due to Ireland's independence movement as well as international factors, such as WWII.
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Central Statistics Office Ireland, & NISRA, & Macmillan Publishers, & Google books, & UN DESA. (June 17, 2019). Population of the island of Ireland from 1821 to 2011 (in millions) [Graph]. In Statista. Retrieved May 12, 2025, from https://www.statista.com/statistics/1014909/population-island-ireland-1821-2021/
Central Statistics Office Ireland, und NISRA, und Macmillan Publishers, und Google books, und UN DESA. "Population of the island of Ireland from 1821 to 2011 (in millions)." Chart. June 17, 2019. Statista. Accessed May 12, 2025. https://www.statista.com/statistics/1014909/population-island-ireland-1821-2021/
Central Statistics Office Ireland, NISRA, Macmillan Publishers, Google books, UN DESA. (2019). Population of the island of Ireland from 1821 to 2011 (in millions). Statista. Statista Inc.. Accessed: May 12, 2025. https://www.statista.com/statistics/1014909/population-island-ireland-1821-2021/
Central Statistics Office Ireland, and NISRA, and Macmillan Publishers, and Google books, and UN DESA. "Population of The Island of Ireland from 1821 to 2011 (in Millions)." Statista, Statista Inc., 17 Jun 2019, https://www.statista.com/statistics/1014909/population-island-ireland-1821-2021/
Central Statistics Office Ireland & NISRA & Macmillan Publishers & Google books & UN DESA, Population of the island of Ireland from 1821 to 2011 (in millions) Statista, https://www.statista.com/statistics/1014909/population-island-ireland-1821-2021/ (last visited May 12, 2025)
Population of the island of Ireland from 1821 to 2011 (in millions) [Graph], Central Statistics Office Ireland, & NISRA, & Macmillan Publishers, & Google books, & UN DESA, June 17, 2019. [Online]. Available: https://www.statista.com/statistics/1014909/population-island-ireland-1821-2021/