Last month was the coldest December for almost three decades as the number of ground frosts also doubled.
Met Eireann's weather report shows that although parts of the east and south were wet for much of the month, it was sunnier than normal everywhere.
Average air temperatures were around two degrees below normal, making it the coldest December for 28 years in much of the country and the coldest month since February 1986 at some weather stations.
Air and ground frost were severe in many places during the second half of last month, particularly over the Christmas period.
There was a total of between 22 and 27 ground frosts during the month at inland stations. The normal range for that time of year is between 13 and 17.
Sunshine totals were above normal everywhere and were well above normal near the Atlantic coast. Most stations had their sunniest December since 2001.