Three are believed dead in the fighting, according to the Department of Justice. Several are known as deadly snipers.
The numbers coincide with earlier reports. An ISIS expert called Abu Omar told Newstalk radio earlier this year that Irish fighters were valued as snipers.
“All the countries around the earth, the Western countries, have fighters with ISIS inside Syria now. There was some of UK people, Irish, French… the Irish fighters are perfect snipers. Every place they need snipers they move the Irish there.
“But the Irish fighters they number around 40.
“They know them from them names as Abu Omar et Irlandais, Irish, Abu Omar Irish.
“They walk in with the British every time, and they see them together.”
He added “Not every individual in this category in this country would have been born into the Muslim community."
He said it was worrying that intelligence services knew nothing of the Paris atrocity plans.
"It is disturbing that this event happened in Paris without some insight by intelligence authorities to indicate that it was going to happen.
"I have no doubt that security services, not just in the UK but in other countries, have foiled similar events," he said.
"We have a duty to the citizens of this country and a common interest with all other countries in Europe to confront and tackle this type of terrorism," he said.