I too got a jury duty mail a couple of years ago. The county office pulls up the drivers license data base. I promptly informed them in writing I am not a US citizen and received an exemptionl letter.
That said many of my immigrant collegues (most of whom have PhDs) never got selected for jury duty. The defense lawyers do not want a rational highly educated person sitting in the jury stand!! The would rather have an average God fearing church going old lady or something like that. But if you are anything but that, well you are not selected!
So, if you don't want to serve make sure that the defense lawyers understand that you are a rational person and not taken in by theatrics and emotions.
One of the partners at my prior place of employment told me that he never gets selected for jury duty because he is a registered Republican.