IT WAS designed to hold 541 inmates, but Columbia Correctional Institute, a brick prison in Portage, Wisconsin, usually houses about 830. New building has helped a bit—metal bunks fill a concrete box added in 1997—but many cells meant to house one inmate now hold two. When there are more prisoners than bunks, as is often the case, beds are laid on the floor.

“This is pretty much typical for the system,” says Gregory Grams, Columbia's warden. Wisconsin's prison population grew by 14% between 2000 and 2007 but, in the same period, the rate of violent crime rose by 23%. By 2019 the number of prisoners is expected to have swollen by another 25%, with a price tag of $2.5 billion.

Facing a $6.6 billion deficit this year, Wisconsin can hardly afford to expand its prison system further. On May 20th a special committee led by Lena Taylor, a state senator, presented draft bills to contain prison costs and improve safety. Jim Doyle, Wisconsin's governor, has proposals of his own within the state budget, which must pass by June 30th.

Wisconsin is not alone. Nearby Michigan, which spent a staggering 22% of its general fund on corrections last year, is debating reforms. Three judges in California have instructed that state to cut its prison population by one-third by 2012. And in Washington, DC, members of Congress are mulling over ways to help state governments curb their prison costs, as well as crime rates.

State correction systems have exploded in recent decades. The Pew Centre on the States, a research outfit, reports that one in 100 Americans is incarcerated. One in 31 is in prison, on parole or on probation. This is expensive. Corrections have gobbled more and more of state budgets, at a faster pace than any government service except Medicaid. In 2008 spending on corrections was 303% greater than two decades earlier.

New laws, not more crime, are the main factor. Since the 1970s, when parole boards had wide discretion to release prisoners, states such as Wisconsin have set mandatory minimum sentences and applied baseball's “three-strikes” rule to the national pastime of incarceration, often locking up repeat offenders for life. In the 1990s federal incentives prodded the states to adopt “truth in sentencing”, meaning that a court sentence would be completed in full, ending rewards for good behaviour behind bars. Mr Grams noted a change both in the time offenders spent at Columbia and in the prison's “climate”, a euphemism for whether inmates behave well or abominably.

Outside the prison walls, rehabilitation and job programmes remain inadequate. In Wisconsin 55% of those in prison in 2007 had been on parole or probation, according to the Justice Centre at the Council of State Governments, a non-partisan group advising the state.

Ms Taylor points to Texas and Kansas as examples of states where reform has begun to reverse these trends. The Justice Centre counselled both states in 2007. The ensuing policy changes expanded treatment programmes in the community and strengthened supervision of those on probation and parole. In Texas the prison population grew by only 529 inmates between January 2007 and December 2008, rather than the 5,141 predicted before reform.

In Wisconsin the governor and Ms Taylor's committee, advised by the Justice Centre, have proposed different plans, but they have much in common. Each would allow an inmate to serve a shorter sentence if he completed certain programmes, such as job training. To keep offenders from repeating their mistakes, each would improve treatments for problems such as mental illness and drug abuse.

The proposals have many critics. Mr Doyle's plan to end “truth in sentencing” has upset Wisconsin's attorney-general and legislators such as Scott Suder, who calls it the “let 'em loose early” scheme. Concern over Wisconsin's deficit may scuttle the committee's proposal, which costs $30m. But the Justice Centre estimates that investing $30m today would avert spending $2.3 billion by 2019.