The Pennsylvania Supreme Court has determined that the right to a jury trial is a procedural right and not a substantive right. In criminal cases, a person is not entitled to a trial by jury in "petty" or summary offenses. This means that if you are facing jail time of less than 6 months, you are not entitled to a jury. If you have a first offense DUI in Bucks County, you are not entitled to a jury trial.
In Bucks County criminal trials with a jury, your jury is comprised of 12 people from Bucks County.
As an aside -- if you are facing a Protection from Abuse order, you do not have a right to a hearing with a jury.