More than 75 per cent of prisoners are aged between 18 and 35, with a majority of them being petty offenders.
An audit report into the country's criminal justice system released Monday by Chief Justice David Maraga, shows a high number of poor people are being jailed compared to the rich.
The report further faults the police for carrying out shoddy investigations, saying some of the cases leading to jail terms should not have ended up in courts.
Releasing the report, Justice Maraga questioned why a majority of young people charged in court for various offences end up in prison when they should be given alternative ways of rebuilding their lives to help decongest prisons.
"It is worrying when more poor people are arrested, charged and sent to prison as compared to the rich. What is worrying more is that majority of those in jail or remand prisons are between 18 and 35 years," said Maraga.
The audit was commissioned by the National Council on the Administration of Justice to analyse the state of affairs of police, courts and prisons when dealing with criminal offences.
The report indicated those with money were likely to bribe their way out when arrested and don't end up being charged or taken to prison.
"Widely varying rates of conversion of arrests into charges suggest a high degree of discretion being exercised by police officers, in both the initial arrest and release, suggesting that Kenyans cannot expect the same treatment," said the report.
Maraga pointed an accusing finger at the police and public prosecutors for their investigations, saying some of the cases in courts should not be there in the first place.
As a result of poor investigations by the police and prosecution, the CJ said 45 per cent of convictions have been overturned or the sentences reduced to lesser punishments when the accused persons file appeals.
The CJ questioned why many people arrested do not end up being charged in court, and that despite records at police stations showing the arrests there are no documentation on the circumstances under which they were released.
"A disturbing fact is 64 per cent of those in police cells had no reason for release recorded in the register or the occurrence book, raising questions on their manner of release. Only 32 per cent of police entries were converted to charges in court, of which 70 per cent were petty offences," he said.
According to the report, petty offenders are likely to be jailed, unlike capital offenses where suspects are either acquitted, matters resolved outside the court or they successfully appeal against the sentences.
It showed that 70 per cent of cases processed through the justice system are offences related to lack of business licenses, being drunk and disorderly and creating disturbance, which can be classified as economically or socially petty.