I asked a retired State Corrections medical director who still consults with prisons: 'In AZ and Federal prisons, are people put into prison populations corresponding to their gender identity or their birth sex? Is it different for men or women? I guess it varies by State?'
'Originally it was based on birth/genital sex. After PREA laws [Prison Rape Elimination Act, signed by George W. Bush in 2003] and a case of surgery in California it is on a case by case basis. Yes it varies State to State.'
'Do they ever put people claiming to be men with vaginas into male populations if the prisoner so requests?'
'No, if pre-op they are put in "protective" housing.'