50 inmates are without a bed in Cork Prison.
The facility on the northside of the city was at 117% capacity at the beginning of the week.
346 people were in Cork Prison which has a capacity of 296 on Monday.
70 prisoners are currently out on temporary release.
The figures are a 10% increase on last year.
The Irish Prison Service says it has no control over the numbers committed to custody at any given time.
It says it makes every effort to find solution when overcrowding occurs and is working with the Department of Justice to ensure a safe working environment for staff, and the safety and security of all those in custody.
