The population of the Irish Republic in 2001 was estimated at 3,840,838, giving the country an overall population density of 55 persons per sq km (142 per sq mi). The population decreased from the 1840s, when about 6.5 million people lived in the area included in the republic, until about 1970, largely because of a high emigration rate. During the 1980s the population increased at an annual rate of only about 0.5 percent. In 2001 the rate was 1.12 percent. Some 58 percent of the population lived in urban areas in 1999.

The constitution provides that Irish, as the national language, is the first official language; it recognizes English as the second official language. All official documents are published in both Irish and English. The modern Irish language, which is very similar to Scottish Gaelic, was widely spoken up to the time of the Great Potato Famine of the 1840s and the subsequent emigrations. From then on, its use declined until 1922, when the teaching of Irish was introduced into all schools. Although its use as a vernacular has decreased and is mainly concentrated in small Gaeltacht (i.e., Irish-speaking) areas, it is certainly more widely read, spoken, and understood today than at any previous time in the 20th century. English is also taught in all the schools and is universally spoken.