Estimates published by the Central Statistics Office suggest that the population of the Greater Dublin Area (GDA) will reach two million by 2021.
The figures are based on a regional breakdown of previously published national population projections and assume that current demographic trends will continue.
The GDA covers Dublin, Meath, Kildare and Wicklow.
The CSO said all regions would experience population growth in the period to 2021, with the mid-east and west showing the biggest increases at 51% and 35% respectively.
The population of the State is projected to grow to just over five million by 2021.