NSW imprisonment rates have skyrocketed to an unprecedented high in the last 12 months despite a drop in crime rates.

In 2013, there were 9,900 prisoners across the state - this year there are 11,000 and this rate of increase is likely to continue.

Contrary to what many fear, crime is not rising and is not out of control. In fact the current government pursued a sound policy over its first two years to reduce the imprisonment rate. This resulted in fewer people in, and returning to, prison; fewer people returning to crime after leaving prison, and reduced spending. Most significantly, it did not result in a rise in crime.

So, if crime isn't rising, why such growth in prisoner numbers?

The NSW Bureau of Crime Statistics in a preliminary analysis, suggests that policing and sentencing practices have changed. Police are arresting and convicting more people, and more offences are now attracting a prison sentence.

The reality is that the majority of people imprisoned haven't committed high-end crimes. They are disproportionately poor. They are disproportionately Indigenous. And they are disproportionately people with mental illness and cognitive impairment, many with low IQs.

Imprisoning a person, locking them in a small cell for the majority of their day and depriving them of liberty is the heaviest penalty we can impose on someone in our society and should be imposed only as a last resort.

Locking people away, even for a short time, is also very expensive.

According to the Productivity Commission, it costs $250 per day to keep a prisoner in NSW. That's a massive $2,750,000 per day to lock up 11,000 people and over 1 billion dollars per year.

Police and court costs add substantially more per offender. Then add legal costs, loss of housing, health and other costs that accrue around a stint in prison and the cost of an average offender being in prison for six months increases to at least $65,000.

At the moment prospects for rehabilitation are poor. NSW has a high recidivism rate: 42% of offenders return to prison within two years with a large number of people moving in and out of the police, court and prison systems at significant cost to the taxpayer.

We need to take a long hard look at the purpose of imprisonment. Does locking up increasingly large numbers of people make for a safe or better society? Are we using the prison to penalise serious crime or to manage social problems?

The US has long used their criminal justice system to deal with problems arising from poverty, lack of mental health services, unemployment and racial discrimination, and the results are staggering. It has the highest imprisonment rate in the world with over two million people in prison, accounting for 25% of the world's prisoners.

They began the 'lock-em-up' policing and sentencing regime NSW has now embarked on, back in the 1980s. Prisons and jails in many states grew exponentially, becoming the dumping ground for mainly young Black and Latino men, largely from poor neighbourhoods with high unemployment and drug use.

In some US states more is spent on prisons than on education. And there is little in the way of rehabilitation or improved safety to show for it. Many are pulling back from this over-imprisonment due to its cost and poor social outcomes.

Instead of spending the money that we currently allocate to policing, sentencing and imprisoning these people, we should be supporting them to live well in the community and $250 a day would go a long way to covering that.

There are towns in NSW with dozens of police but no permanent mental health or disability service. Government would get a far better return for its money by investing in health, education, job creation and support to prevent children and young people becoming repeat offenders.

The onus is on the NSW government to provide us with the evidence that the costs involved in stuffing ever more people into prison are surpassed by the benefits.

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