Prison and jail are not the same thing in the United States.
(It depends on the size and governing body of the facility. If you're sent to prison in the US you are serving state time (usually for serious offences), and if you're sent to jail you are serving county time (probably for a less serious offence). Paris Hilton, for instance, was put in jail, not prison. Of course if you commit a crime in the UK, you'll be slapped on the wrist and told to go to bed early.)