From the summary:
The length of time served in prison has increased markedly over the last two decades, according to a new study by Pew’s Public Safety Performance Project. Prisoners released in 2009 served an average of nine additional months in custody, or 36 percent longer, than offenders released in 1990.
Those extended prison sentences came at a price: prisoners released from incarceration in 2009 cost states $23,300 per offender–or a total of over $10 billion nationwide. More than half of that amount was for non-violent offenders.
– State Fact Sheets: Time Served
– Press Release
– National Survey