The Indian community in Ireland is estimated to be more than three times bigger than the number of people have their nationality as Indian in the last census.
Speaking at the annual Diwali festival of light, Prashant Shukla of the Ireland India Council says many people of Indian origin have taken up Irish citizenship.
He estimated there are around 40,000 members of the Indian community in Ireland.
He added that many others listed as born in countries such as Britain are of Indian origin, while some Irish-born people regard themselves as part of the Indian diaspora.
The numbers giving their nationality as Indian in Ireland dropped by 32% from 2011 to 2016 from 16,986 to 11,465 but this is believed to reflect the fact that many have taken up Irish citizenship.
In the same period the number of people in Ireland who were listed as born in India increased from 17,857 in 2011 to 20,969 in 2016.
Diwali is now considered a global celebration that involves people of all religions, Mr Shukla said.
It is celebrated on the darkest night of the year, which in Ireland was given as last Wednesday.
The festival lasts for five days and a special reception is being held this evening in Dublin's City Hall to mark it.
Taoiseach Leo Varadkar is due to give an audio visual greeting because of other commitments.