At year end 2007, federal and state prisons and local jails held just under 2.3 million inmates (2,293,157). The number of inmates incarcerated in prison or jail increased by 1.5% during the year.
Librarian is an advocate of expanded service to people in jail as an extension of public library service. See “Public Libraries and People in Jail.” RUSQ. Fall 2004. See the excellent overview of Wisconsin students’ service to people in jail by the Jail Library Group.

And especially: Library Services to the Incarcerated Applying the Public Library Model in Correctional Facility Libraries by Sheila Clark, Erica MacCreaigh.