The number of TDs in the next Dáil will increase by no more than two from the current 158 in response to the rise in population revealed by the census.

Minister for Local Government Simon Coveney has established a new Constituency Commission in response to the census figures, with the total number of possible TDs capped at 160.

The preliminary population count of almost 4.76 million revealed by the recent census means that the average number of people per TD for the State as a whole is now 30,114.

This is above the maximum limit set down by the Constitution of one TD per 30,000 people.

After the last census in 2011, it was revealed that five constituencies had more than the prescribed number of 30,000 people per TD, but the national average of 27,598 was still comfortably below the constitutional limit.

In the 2016 census, 25 of the 40 constituencies were above the constitutional limit, pushing the national average over the limit as well.

Article 16 of the Constitution specifies that there must be one TD for between 20,000 and 30,000 of the population.

For most of the State’s history, the figures were close to the lower limit of 20,000, but the rapid rise in population over the past decade has seen a steady rise towards the upper limit.

The constituencies which are most over the limit are Dublin North-West, with 32,299 persons per TD; Dublin Central with 32,016, and Dublin Rathdown with 31,375.

At the other end of the scale, Limerick County has the smallest number of people per TD, with just 27,916 persons per TD.

The fastest growing constituency was Dublin Fingal, which increased by 10,596 persons, or 7.5 per cent, over the five years.

Four constituencies witnessed a fall in their populations: Donegal, Mayo, Sligo-Leitrim and Limerick County.

Commission’s work

The Constituency Commission established by Mr Coveney will redraw constituency boundaries based on the preliminary census returns.

The commission will have until March or April of next year to make its report to the Ceann Comhairle of the Dáil, following the publication of the final census figures at the end of this year.

The commission’s terms of reference are identical to the last commission in 2011, which limited the number of possible TDs to between 153 and 160.

That limit followed commitments by Fine Gael in the 2011 election to reduce the number of TDs.

The rise in population means there will have to be at least 159 TDs in the next Dáil, but the number will probably move up to the maximum of 160 to make the redrawing of constituency boundaries easier.

The number of TDs in the Dáil after independence in 1923 was set at 147. This number was reduced to 138 in 1935 and increased to 147 in 1947.

The first independent Constituency Commission in the late 1970s increased the number of TDs to 166 for the 1981 election.

It remained at that level until 2011, although for much of that period the State’s population was considerably lower than it is now.