Figures from the Irish Prison Service show there were more inmates in Irish institutions than there were beds available yesterday.
The Midlands Prison is overcrowded.
There were 887 prisoners in custody at the facility yesterday, despite only having 875 beds.
Portlaoise Prison was at 95%capacity yesterday - 217 inmates were in custody, according to the Irish Prison Service website.
Nationally, there were nearly 100 more inmates in custody than the 4,409 bed capacity in facilities around the country.
The worst affected is a female institution in Limerick, which was at 136% capacity yesterday.