That's according to the Irish Prison Service's annual report.
The daily average number of prisoners in custody increased by nearly 9% last year.
The Irish Prison Service's Annual Report for 2022 shows there were over 4,100 prisoners in custody every day, compared to nearly 3,800 in 2021.
The Midlands Prison saw an average of 861 inmates every day last year, compared to an overall bed capacity of 875.
While Portlaoise Prison's 231 beds were also almost full every day, with 217 prisoners in custody daily.
The Midlands Prison accommodates the second-highest number of prisoners serving life sentences, at 15.
That figure is nine in Portlaoise Prison, and is being tracked since the introduction of a new model of engagement for people serving life sentences back in 2017.
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