Research from the Central Bank shows that 44% of mortgages or just over 13,000 in long-term arrears are now more than five years past their due date.
That is up from 34% from a year previously.
The figures form part of a review of how bad loans have been handled in the Irish banking system.
The Central Bank thinks just over half of the mortgages in arrears of two years or more may end up with the borrower losing their homes.
There has been a reduction in non-performing loans from a peak of 32% of all loans to just under 14% over the past five years.
Having bad loans on their books reduces the amount of money banks can lend and pushes up the cost of borrowing to consumers and businesses.
That is why the Central Bank and the European Central Bank want to see the level of so-called non-performing loans reduced from just under 14% towards the Euro area average of around 5%.
The banks have been reducing their bad loans, either by restructuring them or by selling off portfolios of loans to so-called vulture funds.
However, the process is slowing down, partly because what is left are the hardest loans to deal with, mortgages in long-term arrears.