705 ILCS 310/9
In other than single county circuits, the chief judge of the circuit court of the county shall certify to the clerk of the court the number of petit jurors required each month. The clerk shall then repair to the office of the jury commissioners or the jury administrator and there, in the presence of the persons mentioned in Section 8 of this act, proceed to draw by lot or by random electronic process the necessary number of names from those made available for such drawing as in Section 8 of this act provided. The clerk shall thereupon certify the electors whose names are so drawn, and summon them by the type of mail service selected from among those permitted for service of petit and grand jurors selected in "An Act concerning jurors, and to repeal certain Acts therein named", approved February 11, 1874, as amended.
If service of summons cannot be made by the type of mail service selected, the clerk of the court issuing such summons shall, as soon as that fact is determined, re-issue and deliver the summons for the juror not served to the sheriff for service as provided in such case in Section 9 of "An Act concerning jurors, and to repeal certain Acts therein named," approved February 11, 1874, as amended. If more jurors are needed during the month, a judge of the court shall so certify, and they shall be drawn and certified forthwith and served in the manner above provided. Whenever a grand jury is required by law or by order of the court, it shall be drawn and certified and served in like manner.
705 ILCS 310/9