The overall figure is up for men and the 18-20s, but down for women
The prison population has grown to a record high of nearly 84,000 in England and Wales - up 66% since 1995.
Statistics from the Ministry of Justice (MoJ) show the population in custody on 30 June numbered 83,900, a rise of 220 from a year earlier.
This was despite more than 60,000 inmates benefiting from an early release scheme introduced in June 2007.
The Howard League for Penal Reform said overcrowded, squalid prison conditions lead to rioting, violence and chaos.
Director Frances Crook said: "As the prison population reaches an all-time high, it is more important than ever to address our failing penal policy.
"Every week we cram hundreds more prisoners into our already bulging jails."
She said prisons were awash with drugs, violence and arson and that the government would inflict this on local communities by building more prisons.
"The answer to rising prison populations is not to build more failing jails," she added.
Tougher sentencing on conviction or when prisoners breached their early release conditions has caused the population increase, according to the MoJ.
Figures for the year to the end of June showed:
- An increase in the number of "lifers" and those doing time for violent and sexual offences
- Falls in the numbers sent down for motoring offences (down 230 - 17%), theft and handling (down 450 - 12%) and fraud and forgery (down 150 - 7%)
- There were 9,800 prisoners aged 18 to 20 - up 2%
- The number of men in custody rose, while the female population dropped 5% to 4,300.
- More than 10% of the total population (8,900 - up 2%) was awaiting trial
Foreign nationals made up 11,400 of those in detention, including people awaiting deportation.
Two years ago, faced with spiralling prison numbers, the government introduced an early release system allowing prisoners to be freed up to 18 days before they were due.
Former Lord Chief Justice, Lord Woolf, criticised the scheme, saying it undermined public confidence in the criminal justice system.
Since then, more than 60,000 prisoners have been released early, with 963 alleged to have gone on to commit further nearly 1,300 offences.
Some 190 also went on the run after being recalled to prison for failing to honour the terms of their release.
But a separate MoJ report said it had "limited impact" because it affected only those serving sentences of under four years.
"The population rose a further 5,900 [between 2005 and 2009] due to lagged effect of previous large increases of offenders on longer sentences," it added.
Shadow justice secretary Dominic Grieve said: "Releasing prisoners early put the public at risk.
"In the next year the number of prisoners released early could rise to almost 100,000. A Conservative government will scrap this disastrous policy," he added.