Synopsis: “Oz” is the nickname for the Oswald State Correctional Facility, formerly Oswald State Penitentiary, a fictional maximum-security prison (level 4) in New York State, given the New York State Flag and motto (“Excelsior”) seen in the background when public officials are shown speaking publicly. There are also references to “upstate”, which is commonly used in New York State. The prison is most likely named after New York Commissioner of Correctional Services Russell George Oswald, who was the head of New York State’s penal system at the time of Attica Prison riot. The character Tim McManus refers to Attica as his hometown and the riot as his original impetus for his wanting to set up Emerald City.

The nickname “Oz” is a reference to the classic film The Wizard of Oz, which popularized the phrase, “There’s no place like home”; in contrast, the series has used the tagline: “It’s no place like home”. (wikipedia)
Oz: The Complete First Season