The amount of time the nation’s criminals spend in prison has risen steadily for two decades. In 2009, the average released prisoner had served just shy of three years, a 36% increase from 1990. As prison stays have increased, so have the costs, to the tune of tens of thousands of dollars per prisoner.

Read: The The States With The Longest Prison Terms

The Public Safety Performance Project, part of the Pew Charitable Trust, released a report examining the duration of prison sentences and stays in 35 states. The report, “Time Served: The High Cost, Low Return of Longer Prison Terms,” measured the average prison sentence for prisoners, the average time served, and the increased costs associated with keeping criminals incarcerated for longer. Based on the report, 24/7 Wall St. identified the states with the longest prison stays in the country.

According to the report, the states with the longest average prison stays, ranging from 3.1 years per inmate to 4.3 years, grew the most in the past two decades. In eight of the 11 states listed here, average time served increased 32% or more. The average increased 83% in Oklahoma and nearly doubled in Virginia. Of these states, eight were among the 15 with the largest increases.

Reasons for the increase vary, according to Adam Gelb, director of the Public Safety Performance Project. In recent years, some states have passed legislation that increases how much each prisoner serves of his or her sentence. Also, parole boards have been more reluctant to release prisoners, regardless of the laws.

However, according to Gelb, the biggest driver is the belief that longer prison terms reduce recidivism. Unfortunately, Gleb says that it does not appear to work. “For a substantial number of non-violent offenders, there is little or no evidence that keeping them locked up longer prevents crime or keeps them from re-offending once released from prison,” Gleb reports.

The average cost of keeping a prisoner locked up varies widely. In Oklahoma, it is estimated to cost the state $1,529 per month. In Oregon, the monthly bill is $5,304. Even at the lower end of the cost spectrum, these costs add up.

States spend tens of thousands of dollars more now than in 1990 because prisoners serve an average of nine additional months. In Michigan, the average time served grew by 23 months, more than any other state, or $53,247 more for the additional prison time. It is estimated that, of the prisoners released in 2009 alone, the state spent $471.9 million more than it would have if the average stay was still at 1990 levels.

The Pew report also broke out the costs resulting from increased prison stays into three major types of crime. Since 1990, the length of stay for those committing property crimes, such as theft and burglary, increased 24%. Time served for drug-related crimes and violent crime rose more, with 36% and 37% increases, respectively. The average period of incarceration for violent crimes, which include murder, assault and robbery, increased from 3.7 years to five years. In Michigan, average incarceration time for these kinds of crimes increased from 3.6 years to 7.6, the longest stretch in the United States.

In addition to the average time served and costs associated with the additional time, 24/7 Wall St. examined recidivism rates by state, obtained from another Public Safety Performance Project report, titled “State of Recidivism: America’s Revolving Door.” Violent crime rates are based on the FBI’s Uniform Crime Report.

These are the states with the longest prison stay in the country.

11. Hawaii
> Average time served in 2009: 3.1 years
> Change in length of stay from 1990: -15%
> Cost to state of keeping prisoners longer: -$27.7 million

In Hawaii, the average time served for prisoners released in 2009 declined by seven months, or 15%, from 1990. However, Hawaii has increased average time served for the most serious offenders, as violent criminals released in 2009 served an average of 6.2 years, the second-highest average for any state in the survey. Those convicted of property crimes and drug crimes in Hawaii received similarly harsh sentences, as time served by property crime offenders averaged 3.3 years while time served by drug crime offenders averaged of 2.9 years. These figures were the highest and second-highest state averages, respectively.

10. New Hampshire
> Average time served in 2009: 3.1 years
> Change in length of stay from 1990: 26%
> Cost to state of keeping prisoners longer: $14.5 million

The average cost of imprisoning a criminal under the New Hampshire penitentiary system is $2,840 per month, according to the most recent data. That is the 13th highest in Pew’s survey. Average time served per inmate has increased by eight months since 1990, contributing to the climbing prison population and costs in New Hampshire. The state has one of the lowest incidences of violent crime, about a third of the national rate. However, average time served for a violent crime has increased by 45% since 1990. Keeping offenders out of prison is also an issue in New Hampshire — prisoners released between 2004 and 2007 had a recidivism rate of 44.2%, the 10th highest.

9. West Virginia
> Average time served in 2009: 3.1 years
> Change in length of stay from 1990: 51%
> Cost to state of keeping prisoners longer: $74.8 million

According to the latest Pew data, the average West Virginia inmate released in 2009 served 3.2 years in prison for property crimes, nearly a full year more than the national average. This is more than double the average time served for those released in 2000 in the state. Overall, the average prison stay in West Virginia increased by roughly a year between 1990 and 2009. Pew estimates that increased stays cost the state roughly $27,708 per prisoner, or nearly $75 million for all prisoners released in 2009.

8. Oklahoma
> Average time served in 2009: 3.1 years
> Change in length of stay from 1990: 83%
> Cost to state of keeping prisoners longer: $203.9 million

In 1990, the average length of stay for Oklahoma’s prisoners was just 1.7 years, well below the national average of 2.1 years. By 2009, the average time served by a prisoner had increased by 17 months. Much of this appears to have been driven by increases in the amount of time prisoners served for property and drug crimes. A typical inmate released in 1990 could expect to serve 1.5 years for a property crime and 1.2 years for a drug crime. For those released in 2009, these averages had risen by 93% and 122%, respectively, to 2.9 years and 2.6 years. These increases in prison stay also cost taxpayers, as the state spends $25,636 more for each prisoner kept 3.1 years instead of for 1.7 years.

7. Oregon
> Average time served in 2009: 3.2 years
> Change in length of stay from 1990: 32%
> Cost to state of keeping prisoners longer: $121.5 million

According to Pew, Oregon had the lowest recidivism rate in the country for prisoners released between 2004 and 2007. Just 22% of those released in that time returned to prison, compared to a national average of 43.3%. While recidivism remains low, the length of time served increased 32% to 3.2 years.

6. Arkansas
> Average time served in 2009: 3.2 years
> Change in length of stay from 1990: 69%
> Cost to state of keeping prisoners longer: $305.1 million

Of all states surveyed, none is tougher on drug offenders than Arkansas, where the average prisoner released in 2009 served three years. This represented a 122% increase from 1990, when the average prisoner served just 1.4 years for a drug offense. Time served for drug crimes has increased every five years for the past two decades. Yet, while the state seems to have focused on punishing drug-related crimes, it also has some of the highest rates of violent and property crime in the nation.

5. Georgia
> Average time served in 2009: 3.2 years
> Change in length of stay from 1990: 75%
> Cost to state of keeping prisoners longer: $536.1 million

The average prison time served in Georgia has increased by 75% since 1990, making it the sixth-largest percentage increase. Prisoners incarcerated for drug-related crimes in Georgia could serve 85% more time in 2009 than they would have in 1990. Those serving for violent criminal offenses spent an average of 5.6 years behind bars, 12% more time than the national average. The increased length of time served has resulted in an increased cost of $28,563 per inmate for a total of $536.1 million.

4. Virginia
> Average time served in 2009: 3.3 years
> Change in length of stay from 1990: 91%
> Cost to state of keeping prisoners longer: $518.8 million

The average prisoner released in Virginia in 1990 had served just 1.7 years — well below the then-national average of 2.1 years. By 2009, Virginia’s average time served had increased by 91% to 3.3 years, the second-highest percentage increase in the nation. Much of this increase was driven by a rise in the percentage of sentences served: from 1990 to 2000 the length of sentences served rose 71% for violent crimes and 116% for nonviolent crimes. This trend continued from 2000 to 2009, when the length of sentences served rose another 18% for violent crimes and 10% for nonviolent crimes. Such policies are extremely expensive. Simply keeping those prisoners released in 2009 incarcerated for longer cost more than a half a billion dollars.

3. New York
> Average time served in 2009: 3.6 years
> Change in length of stay from 1990: 2%
> Cost to state of keeping prisoners longer: $65.6 million

New York was the only state on this list that decreased incarceration time for both drug and property crimes. But between 1990 and 2009, the average length of prison stay for violent crimes increased by 24% to six years, a full year longer than the national average. With the second-highest nationwide cost per month of imprisonment, at $5,006 per inmate, decreasing detention length could help the state save millions in correctional facility costs. Keeping offenders in prison longer has cost New York $65.6 million, a relatively small amount given the increased cost per month.

2. Pennsylvania
> Average time served in 2009: 3.8 years
> Change in length of stay from 1990: 32%
> Cost to state of keeping prisoners longer: $316.6 million

In 1990, time served in Pennsylvania for violent, property and drug crimes were already comparatively high. By 2009 the average length of stay had reached 5.9 years for violent crimes, 2.9 years for property crimes and 2.8 years for drug crimes. These increases were due largely to changes in the percentage of sentences served, as sentence lengths have increased only marginally in the past 10 years. According to Pew, this was partially the result of changes in how prisoners received parole. In 1994 it took one vote from a five-person board to receive parole, but by 1996 five out nine votes were required to receive parole.

1. Michigan
> Average time served in 2009: 4.3 years
> Change in length of stay from 1990: 79%
> Cost to state of keeping prisoners longer: $471.9 million

Michigan has the longest average incarceration among all states surveyed, with an average time served of 4.3 years. That is almost half a year more than any other state and three years more than South Dakota, the state with the lowest length of stay. Michigan imposes especially long prison sentences for violent crimes, which carry an average time served of 7.6 years, a full 2.6 years more than the national average. The state also imposes long sentences for drug crimes, as the average time served was 2.9 years for prisoners released in 2009, tied for the second-highest average. This commitment to the state’s penal system has been especially expensive, as the state spent $53,247 to keep the average prisoner incarcerated for an additional 23 months. This average extra cost per prisoner was greater than in any other state in the nation.

Michael B. Sauter, Alexander E. M. Hess and Lisa Nelson

Thank you for reading! Have some feedback for us?
Contact the 24/7 Wall St. editorial team.