New census figures from the Central Statistics Office show that the five major cities - Dublin Cork, Limerick, Galway, and Waterford - have been losing population share as a group compared with the rest of the country.
The five grew by only half the rate of the whole country in the four years between 2002 and 2006.
Galway was the only city of the five to buck this trend with population growth of almost 10% in the four years. If Galway were to continue growing at this rate, the city could reach a population of 100,000 by 2020.
Outside of the main cities there was also a sharp growth in the population of large towns with 10,000 people or more.
The census figures show that the number of these towns has increased from 28 to 34 in the space of four years, with Drogheda now the fifth largest town in the country, followed in order by Dundalk, Swords and Bray. The six new large towns include Mallow, Wicklow, Arklow, Cobh, Midleton, and Ballina.
Today's figures also show that the population of Balbriggan in Co Dublin has grown by 51% in four years. The data also reveal an extremely strong growth in the population of Blanchardstown-Blakestown electoral district of Dublin West, where the population has b grown by 8,000 in three years and now stands at 32,300.
According to the Constitution, an additional TD may now be justified for the area.