Over 1.6 million Irish people claim they can speak the Gaelic language but the proportion of native speakers dropped from 42.8 to 41.9 percent between 2002 and 2006, according to the Census data.
Schoolchildren were by far the most likely to speak Gaelic but figures from the Central Statistics Office (CSO) shows fluency declined when people left school.
Of the 1.66 million people who indicated in the 2006 Census that they could speak Gaelic, just over a million either never spoke the language or spoke it less frequently than weekly.
Nearly half a million people said they spoke Gaelic on a daily basis at school but this plummeted to some 72,000 -- 4.4 percent of all those who can speak Gaelic -- who spoke it on a daily basis outside education.
Under Ireland's 1937 constitution, Gaelic is recognised as the first official language. In June 2005, the EU made Gaelic the 25-nation body's 21st official working language.
Last year, in the first major policy statement on Ireland's Gaelic language in more than 40 years, Prime Minister Bertie Ahern unveiled a 20 year strategy to create a bilingual society.
He said the "aim of 20th century government policies was to reinstate Irish as the main language spoken by the people."
But the new figures will be a disappointment.
Even in most of the special so-called Gaeltacht areas, where dwellers receive extra grants and allowances for schools, homes, clubs, and festivals to encourage Gaelic speaking, the numbers are down.
Most of the Gaeltachts are scattered along the western seaboard.
Gaelic was the country's predominant language up until the middle of the 1800s.
British colonisers introduced English as the sole language of government and it became dominant in the bigger cities.