The Republic of Ireland has a population of approximately 5.1 million people as of 2023, while Northern Ireland adds another 1.9 million to the island total of roughly 7 million inhabitants. This represents a demographic recovery after centuries of decline—the island's population peaked at approximately 8.5 million in 1841 before the Great Famine began. Ireland remains one of the few European countries whose current population has not yet reached its pre-famine levels. The population is concentrated in the east, with Dublin and its surrounding counties containing approximately 1.9 million people, more than one-third of the Republic's total. The Republic maintains one of the youngest populations in Europe, with a median age of 38.8 years as of 2022, compared to an EU average above 44 years. Net immigration has returned to positive levels since the 1990s after more than a century of net emigration, with significant populations arriving from Poland, Lithuania, Romania, and Brazil since EU expansion in 2004.
The Irish Travellers constitute the island's indigenous ethnic minority, numbering approximately 40,000 people across the island according to census data. This population maintains distinct cultural practices including nomadic or semi-nomadic traditions, their own language variety called Shelta or Cant, and social structures centered on extended family groups. The Irish government officially recognized Travellers as an ethnic minority in 2017, though discrimination in housing, employment, and education access remains documented through studies by the Economic and Social Research Institute. Traveller life expectancy at birth measured 11 to 15 years below the national average in 2019 studies, and infant mortality rates remain approximately three times higher than the settled population. Traditional Traveller occupations included tin-smithing, horse trading, and seasonal agricultural work, though mechanization and economic changes have reduced these opportunities. Approximately 80 percent of Irish Travellers now live in houses rather than caravans, though many maintain the practice of traveling during summer months.
Ireland's religious composition transformed radically between 1961 and 2022. The Republic's 2022 census recorded 69 percent identifying as Catholic, down from 95 percent in 1961. Those identifying with no religion increased from 0.04 percent in 1961 to 14 percent in 2022, making it the second-largest category. Church of Ireland membership stands at approximately 2.5 percent of the Republic's population. In Northern Ireland, the 2021 census showed Catholics at 45.7 percent and Protestants and other Christians at 43.5 percent, the first time Catholics outnumbered Protestants since partition in 1921. Weekly Mass attendance in the Republic fell from approximately 91 percent in 1973 to 36 percent in 2011 to an estimated 25 percent by 2019, according to surveys conducted by the Association of Catholic Priests. This decline accelerated following revelations about institutional abuse in Catholic-run schools, mother and baby homes, and Magdalene Laundries documented in the Ryan Report of 2009 and subsequent investigations. The 2015 marriage equality referendum passed with 62 percent support, and the 2018 abortion referendum passed with 66 percent support, marking clear departures from Catholic social teaching in law.
The Irish language, called Gaeilge, is the first official language of the Republic under Article 8 of the Constitution, though English functions as the predominant language in daily life. The 2016 census recorded 1.76 million people claiming some ability to speak Irish, representing 39.8 percent of the population, but daily speakers outside the education system numbered only 73,803 people. The Gaeltacht regions—officially designated Irish-speaking areas primarily in western coastal counties including Galway, Donegal, Kerry, Cork, and Mayo—contained approximately 96,000 people as of 2016. Even within these regions, the 2011 Comprehensive Linguistic Study of the Use of Irish in the Gaeltacht found that only 24 percent of Gaeltacht residents spoke Irish daily. All children in the Republic study Irish as a compulsory subject from primary through secondary school, though functional fluency rates among graduates remain low. TG4, the Irish-language television channel established in 1996, broadcasts entirely in Irish with English subtitles. Ulster Scots, spoken primarily in parts of Northern Ireland, received recognition under the European Charter for Regional or Minority Languages in 2001, though speaker numbers and linguistic boundaries remain contested, with estimates ranging from 30,000 to 100,000 people claiming some familiarity.
The arrival of farming to Ireland occurred between 4350 and 4050 BCE based on radiocarbon dating of Neolithic settlement sites and domesticated grain remains. These first farmers built court tombs and passage tombs, with Newgrange in County Meath representing the most sophisticated example. Newgrange was constructed approximately 3200 BCE, making it older than Stonehenge and the Egyptian pyramids at Giza. The structure consists of approximately 200,000 tons of stone and contains a 19-meter passage aligned so that sunrise on the winter solstice illuminates the inner chamber. The Bronze Age in Ireland began approximately 2500 BCE with the appearance of copper and gold working, evidenced by hundreds of gold lunulae and torcs in museum collections. Iron Age culture arrived approximately 500 BCE with Celtic peoples, though genetic studies published in 2015 showed that modern Irish DNA derives primarily from earlier populations rather than Celtic migrants, suggesting cultural transmission rather than population replacement.
Christianity arrived in Ireland during the fifth century CE, traditionally associated with St. Patrick though documentation remains sparse and contested. The earliest secure written reference to Patrick comes from his own Latin writings, the Confessio and the Letter to Coroticus, dated to the mid-to-late fifth century. Patrick describes his capture from Britain as a youth, his enslavement in Ireland for six years, his escape, and his later return as a missionary. The specific year 432 CE commonly given for his arrival comes from later medieval sources rather than contemporary documentation. Monastic Christianity became the dominant organizational form in Ireland rather than the episcopal structure common elsewhere in Europe. Major monasteries at Clonmacnoise, Glendalough, Clonard, and Bangor became centers of learning and manuscript production during the sixth and seventh centuries. Irish monks established monasteries across Europe, including Columbanus at Luxeuil and Bobbio, and Columba at Iona. The Book of Kells, an illuminated manuscript of the four Gospels, was produced around 800 CE, likely at Iona or Kells monastery.
Viking raids began in 795 CE with the attack on Lambay Island near Dublin, documented in the Annals of Ulster. Norse Vikings established longphorts—fortified ship harbors—that developed into Ireland's first true towns at Dublin around 841, Waterford around 914, Wexford, Cork, and Limerick. These settlements introduced urban mercantile culture to an island previously organized around rural monasteries and túatha—small kingdoms. Brian Boru, king of the Dál gCais dynasty, defeated a coalition of Leinster Irish and Dublin Norse at the Battle of Clontarf on April 23, 1014, though Brian himself died in the battle. Clontarf ended Norse expansion but did not expel Norse populations, who remained as integrated urban merchants. Ireland at this time comprised approximately 150 separate túatha grouped under several provincial kingdoms, with no single unified authority.
The Norman invasion began on May 1, 1169, when Robert FitzStephen landed at Bannow Bay in County Wexford with approximately 390 men. This force came at the invitation of Diarmait Mac Murchada, deposed king of Leinster, who sought military aid to regain his kingdom. Richard de Clare, called Strongbow, arrived in 1170 with a larger force and married Mac Murchada's daughter Aoife. When Mac Murchada died in 1171, Strongbow claimed Leinster. King Henry II of England, concerned about the creation of an independent Norman realm, arrived in October 1171 with a large fleet at Waterford and received submission from most Norman lords and many Irish kings. The Treaty of Windsor in 1175 between Henry II and Ruaidrí Ua Conchobair, High King of Ireland, attempted to establish boundaries between English-controlled Leinster and Irish-controlled areas, but Norman expansion continued incrementally. By 1300, approximately two-thirds of Ireland was under Norman control, though extensive intermarriage and cultural adoption led to the Gaelicization of many Norman families. The Statutes of Kilkenny in 1366 attempted to prohibit English settlers from adopting Irish language, dress, and customs, indicating how widespread such adoption had become.