Police have lost track of 485 registered sex offenders across Britain, according to a report.
The missing include rapists and paedophiles, including some who disappeared more than a decade ago, according to a Sky News investigation.
Forces across the UK were asked to reveal the number of registered sex offenders whose whereabouts were unknown on 17 January.
Figures released by the number of convicted sex offenders whose whereabouts are unknown in the Calendar region is at least 40.
- Derbyshire Police
The force said there were seven registered sex offenders whose whereabouts were unknown.
One had been missing since June 2006, two had been missing since February 2008, one since January 2012, one since May 2010, one since January 2012 and one since September 2017.
Offences include rape, indecent assault of a boy under 14, sex assault on a child under 13, gross indecency with a girl and sexual assault of a boy under 13.
- Humberside Police
The force said the whereabouts of nine registered sex offenders were unknown.
One has been missing since 2008, one since 2010 and another since 2011.
- Lincolnshire Police
The force said there were four registered sex offenders whose exact locations were unknown - all of which are believed to be outside the UK.
One had been missing since 2006, one since 2014, one since 2015 and another since 2016.
Their offences included rape, indecent assault and possession of indecent images.
- South Yorkshire Police
The force said 10 registered sex offenders were wanted because their whereabouts were unknown.
- West Yorkshire Police
The force said there were 10 registered sex offenders wanted for breaching of registration requirements.
Three of the offenders are known to be living outside the UK and four offenders have been wanted for more than a year.
Alex Mayes, from charity Victim Support, said: "These figures will potentially be very alarming to victims of sexual offences and could undermine public confidence in the criminal justice system.
"To ensure the safety and well-being of survivors of sexual offences, as well as local communities, it is vital that the police strictly monitor sex offenders."
Registered sex offenders must inform police of their addresses and are subject to monitoring by authorities who manage certain sexual and violent criminals living in communities.
There were a total of 55,236 registered sex offenders living in England and Wales in 2016/17, according to a Ministry of Justice report published last October.
A Home Office spokeswoman said: "The UK has some of the toughest powers in the world to deal with registered sex offenders and we are committed to ensuring that the system is as robust as it can be.
"We have significantly strengthened the system of reporting that sex offenders are subject to, and a range of civil orders have given police more powers to manage their behaviour.
"When a registered sex offender goes missing, their details are recorded on national and international systems and the police will actively seek out further information and intelligence to locate them."