The Department of Social Protection has launched investigations into 3,260 cases of suspected welfare fraud this year.
Figures released through Freedom of Information (FOI) show 7,316 reports were received by the department up to the end of June.
This compares to 14,363 investigations in 2017 and 9,791 in 2018.
The highest number of criminal cases relate to Jobseekers Allowance.
The department says criminal prosecutions are taken against persons who defraud the social welfare payments system, and employers who fail to carry out their statutory obligations.
Some 41 cases have been referred to the Chief State Solicitors Office.
A separate 53 criminal cases were finalised in court - 45 of whom were convicted, with two jailed.
The department says it finalised 165 criminal cases in court during 2017.
The value of overpayments associated with these was some €4.7m.
While in 2018, it took 171 criminal cases worth €4.4m.
The figures show €39.2m has been refunded to the department so far this year as a result of overpayments, or fraudulently obtained welfare payments.