The team used the latest forensic techniques that would detect even the tiniest fragments to study a batch of 45 used banknotes.
The scientists at Dublin's City University said they were "surprised by their findings".
Some of the notes had such high levels of cocaine on them that it is thought they were used to snort the drug.
Others had much lower traces and may have been cross-contaminated, perhaps in the wallets or pockets of users.
Growing cocaine use
The results fit with scientific findings from other countries such as the UK and Spain where cocaine has also been found on a high proportion of notes.
Cocaine particles stick to the cotton that is contained within the notes.
Cocaine use is thought to be growing in Ireland. Professor Brett Paul, whose paper was published in a journal of the Royal Society of Chemistry in the UK, said it demonstrated how widespread the use of cocaine is.
The study also found that higher value banknotes, such as 20 and 50 euros, were more likely to contain greater traces of the drug.
In recent weeks there has been fresh focus in Ireland on the use of drugs in society.
Dublin has seen a number of murders that have been linked to drugs gangs and Ireland's justice minister has said that those who buy cocaine are helping to finance such groups.
One newspaper editorial said that the trend of cocaine use showed that there is something rotten at the heart of Ireland's economic boom.
