According to the Law Dictionary, federal facilities maintain searchable databases of prisoners complete with updated information about their sentences and release dates while smaller local prisons often must be contacted via telephone or email in order to find such information. It is relatively easy to find an inmate's release date, as the information is in the public domain by definition.
Knowing where the prisoner is incarcerated is the single most relevant piece of information. It goes a long way toward finding information on a given prisoner.
Use name and prisoner ID
Contacting a prison with an inmate's name and prisoner ID number is an easy way to find information on that prisoner. Facilities will release information such as release dates to most parties in possession of such information.
Query local prisons
Local prisons do not always have online databases. This means that the easiest way to find information about inmates and releases dates is to write or call, and then provide prisoner information to the appropriate authorities.
Search federal databases
Federal penitentiaries list their inmates online. Users with the right information, including name and prisoner ID number, can find any given inmate within the federal system and also ascertain information like when that prisoner's release date is set.