It means a fresh headache for the Constituency Commission, which redrew the electoral map for this year’s general election to cut constituency numbers from 43 to 40 and the number of TDs from 166 to 158.
By law, the population-TD ratio cannot exceed 30,000-1 and based on the 2011 Census, 158 was enough seats to provide a TD for every 29,000 people. The new Census puts the average at 30,114.
“We’re handing the data file over [to the Commission) tomorrow and they will begin their deliberations in redrawing the constituencies. Clearly there will have to be at least one more TD now to bring it back to 30,000,” said Deirdre Cullen, CSO senior statistician.
In the past, census results have shown up several constituencies with ratios that breach the law but this time 25 constituencies are in breach, which is believed to be unprecedented.
Dublin North-West, which changed from a four-seat to a three-seat constituency in 2002, and which is home to Social Democrat TD Róisín Shortall, Sinn Féin’s Dessie Ellis, and Fine Gael’s Noel Rock, has the greatest excess with 32,299 people. It is followed by Dublin Central, 32,016; Dublin Rathdown, 31,375; Galway East, 31,300 and Cork North Central, 31,200.
Limerick County has the fewest people per TD with 27,916, followed by Clare, Roscommon-Galway, and Cork South-West, all with fewer than 28,500.
Deciding where to create an additional seat or seats will not be as simple as choosing from the areas with the current biggest ratios, as population trends will have to be taken into account. From that perspective Dublin Fingal is the fastest growing, up 7.5% in five years, meaning constituency boundaries are likely to have be redrawn again.
Ms Cullen said that the CSO’s annual population estimates had been lower than the Census now shows them to be.
“Clearly over the five years we have been underestimating immigration and possibly overestimating emigration. They are notoriously difficult to measure.”
‘To hell or to Leinster’ as migration goes east
An east-west divide in population trends is starkly illustrated by the Census 2016 which shows the strongest growth concentrated almost entirely in Leinster.
Dublin’s four administrative areas recorded increases of 4.8% to 8.1% while its commuter belt counties grew as follows: Meath (5.9%), Kildare (5.6%), Louth (4.5%), and Wicklow (4.2%).
The influence also stretched out a bit further to neighbouring counties Longford (4.6%), Carlow (4.1%), and Cavan (4%).
Outside this region, the most significant areas of growth were the cities of Cork (5.4%) and Galway (5.3%). Cork county (4.2%) was also above the 3.7% national figure, but the only other pocket of growth to exceed that was Kilkenny (3.9%).
Cork, Limerick, Waterford, and Galway cities all grew faster than their surrounding counties but the biggest turnaround was in Cork City, where the population had dropped by -0.2% between 2006 and 2011 and is now up by 5.4%.
Population fell in three counties: Donegal (-1.5%), Mayo (-0.2%), and Sligo (-0.1%) and there were very small increases in Leitrim (0.5%), Roscommon (0.6%), and South Tipperary (0.7%).
Next was Clare (1.2%), Monaghan (1.3%), Kerry (1.4%), Waterford county (1.4%), north Tipperary (1.5%), Limerick county (1.6%), Offaly (1.7%), Galway county (2.2%), Westmeath (2.6%), and Wexford (2.9%). The population of Waterford city grew 3.5% and Limerick city 2.1%.