Last month was the coldest December for almost 30 years over most of the country, Met Éireann has said.
In its monthly summary, the forecaster said December was the coldest month for 28 years for most of the country and the coldest of any month since February 1986 at a few stations.
The forecaster said there was a total of between 22 and 27 ground frosts during the month at inland stations, compared with the normal range for December of between 13 and 17.
The lowest temperatures of the year were recorded in late December, when Mullingar’s air and ground temperatures hit -10.0°C and -13.0°C respectively on December 25th.
However, sunshine totals were above normal during the month, with most stations having their sunniest December since 2001 according to the statistics.
The lowest ever in Ireland was -19.1 at Markree Castle, Co Sligo on January 16th, 1881 while the lowest observed 20th century air temperature was -18.8°C recorded at Lullymore, Co Kildare on January 2nd, 1979.
Age Action urged people to continue to look out for older neighbours and relatives unable to leave their homes because of the cold snap.
“With the sub-zero temperatures forecast to continue for the coming days, older people who are house-bound by the weather and who have not been receiving regular visits over the holiday period may be in difficulty when it comes to supplies of food, fuel and medicine," spokesman Eamon Timmins said.
“We are urging people to call in to their older neighbours to ensure they are safe and well "You cannot presume that another neighbour will do this - they could be expecting you to do it.”
The charity said it has received calls from elderly people unable to leave their homes for up to four weeks because of icy conditions.
“While local authorities have worked to make the main roads safe, footpaths, especially in residential areas, remain treacherous,” Mr Timmins said.
“Regardless of what preparations older people had made for the unusual winter cold snap, nobody would have adequate food and medical supplies to enable them get through the period of weather we are currently experiencing.
“Unless their friends, neighbours and relatives contact them, some older people could find themselves in real difficulty.”