A total of 17,318 prison committals were recorded last year, the latest report from the Irish Prison Service shows.
This is a 0.8% increase on the total in 2010.
13,952 persons were sent to prison, several thousand of them more than once. 86.4% of those committed in 2011 were men and 13.6% were women.
Publishing the Annual Report, Minister for Justice Alan Shatter said that the greatest challenge facing the prison service is the increasing number of prisoners being committed to custody.
However, the minister said the latest figures compared with increases of 11.4% and 13.8% in the previous two years.
Just under half off all committals were for periods of less than three months, up by 10%. The numbers of prisoners serving sentences of between three and five years increased by 12.4%.
The average cost of a prison space for 2011 was €65,359.
On any given day, there are around 4,500 people in custody across the State.
Nine out of ten prisoners are Irish nationals. 291 were serving life sentences and another 290 are serving sentences of more than 10 years.
The Irish Penal Reform Trust welcomed the "levelling off" of prison numbers, given that the number of prisoners had increased by over 30% over the preceding three years.
But it expressed concern about the increase in women being sent to prison - 200 more were sent to prison in 2011 than in 2010 - and the use of prison for fine defaulters.
Some 423 committals in 2011 related to immigration issues, a decrease of 13.9% on 2010. That followed a dramatic drop of 31% in this category in the previous year.