The Oswald State Correctional Facility (previously Oswald State Penitentiary) is a maximum security prison which seems to be located in the state of New York (given the New York state flag and motto seen in the background when public officials are shown speaking publicly, references to "upstate", a term commonly used in New York, the prisoner flashbacks seemingly having New York City as a backdrop, and the format of the prisoner ID numbers).
It is never made clear how long Oswald has been around, but it is shown to at least date back to 1943, according to Ricardo Alvarez' crime flashback. Emerald City also seems to be a fairly new unit compared to the others. Both Whitney Munson and Ricardo Alvarez seem to have been in Oswald for the longest amount of time (both convicted in the early 1940s).
The prison is run by Warden Leo Glynn throughout the majority of the show's run. Martin Querns takes over as warden in Season 6.
Many parts of Oz were rebuilt after a gas explosion, though only a few of them are ever seen, or mentioned directly, in the series.
- Emerald City - (Also referred to as "Em City") An experimental unit managed by Tim McManus. Redecorated after the gas explosion.
- Unit B - General population cell block of Oswald State Correctional Facility.
- Unit C - Mentioned by Kareem Said in reference to Reggie Rawls being a major drug dealer there.
- Unit E - The AIDS ward of Oswald State Correctional Facility.
- Unit J - A small cell block made mainly for former police officers and other authority figures.
- Death Row - A cell block for incarcerated inmates pending death in Oswald State Correctional Facility.
- Administrative Segregation - (Also referred to as "The Hole" and "Ad-seg") A cell block where prisoners are confined in an empty cell, and stripped naked, as a punishment for misbehavior.
- Solitary Confinement - Where prisoners are isolated for a certain amount of time for severe offenses.
- Protective Custody - The special placement of prisoners that are evidently in danger.
- Gym - Monitored, indoor recreation area for prisoners. The weights are used as makeshift weapons in several cases.