A state prison inmate locator would allow a searcher to find an inmate who is within a particular state's prison system. A state prison inmate search service would inherently have to be a different individual service for each state, as each state has a separate Department of Corrections and would thus have a separate state prison system.
There are some state prison inmate locator services which serve as aggregates of the different state prison inmate search services available from each state, thereby allowing a search of all states from one website, but these services are sometimes suspect and not necessarily as effective as simply using the state prison inmate locator for that particular state.
A state prison inmate search service will generally allow searchers to look for an inmate using several different pieces of information, including name, birth date, and information about that inmate's status within the Department of Corrections, such as that individual's department ID number. Different states may allow for slightly different search criteria, particularly as different states might have different ID systems set in place.
Some state prison inmate search services might provide additional information as well, such as the parole status of an inmate, though this varies from service to service. Additionally, the state prison inmate locator service for a particularly populous state might be updated more frequently, whereas a smaller state's state prison inmate search service might be updated less frequently, thus either accordingly increasing the utility of that service or decreasing the utility.