It has emerged that a remand prisoner in the Dochas Centre in Dublin tested positive yesterday.
The case was detected as part of the routine testing of new committals.
The woman had been in quarantine since she came into the prison ten days ago.
There are 107 prisoners in the Dochas centre and 3,700 inmates are in jail in Ireland.
The Irish Prison Service says confirmation of any case of Covid is a matter for NPHET or the HSE.
Prisons were highlighted as a concern earlier in the pandemic, with visiting restrictions introduced to reduce the likelihood of the virus entering facilities around the country.
These visiting restrictions were relaxed earlier this week, except in Portlaoise and the Midlands prisons due to a regional lockdown in Laois.
The relaxation allows for a prisoner to see one family member every two weeks.
The Irish Prison Service had earlier been commended by the World Health Organisation for keeping the virus out of the prison service here.
