Why am I required to do jury service? Learn all that you need to know after responding to a jury summons to serve as a member of the jury in Maricopa County.What is the difference between a petit jury and a grand jury? A petit jury is a trial for civil and criminal cases. Your role as a juror is to get a full understanding of the facts of a criminal case, to evaluate the evidence, and to make an impartial and fair decision. All US citizens are qualified for jury service if they are at least 18 years old, are residents of the jurisdiction in which they have been summoned to serve. Information for Jurors. Potential jurors must complete the juror qualification questionnaire. The following is a brief description of the process to prosecute an adult accused of committing a felony offense. Can I complete my Juror Affidavit Questionnaire on-line instead of mailing it?