705 ILCS 305/9
In other than single county circuits, if a grand jury is required by law or by the order of the judge for any court, the county board in each of the counties in this State wherein such court is directed to be held, at least 20 days before the time of appearance specified in the summons hereinafter mentioned shall select 16 persons possessing the qualifications provided in Section 2 of this Act, by lot from the jury list, to serve as grand jurors; the panel of the 16 persons so selected to be known as the regular panel; and shall at the same time, in like manner, select 12 additional persons possessing such qualifications, the panel of the 12 additional persons so selected to be known as the supplemental panel; and cause their clerk within 5 days thereafter to certify the 2 panels properly identified as the regular panel and supplemental panel, respectively, to the clerk of the court for which they are selected, who shall issue a summons to each of the 16 persons so selected for the regular panel, at least 10 days before the time hereinafter mentioned, commanding him to appear before such court at or before 11:00 a. m. upon the date of appearance of the grand jurors established pursuant to Section 112-3 of the "Code of Criminal Procedure of 1963", approved August 14, 1963, as now and hereafter amended, to constitute a grand jury. The clerk of the court issuing such summons shall follow the procedure he selects or is directed by the court to select from among those permitted by this Section.
The issuing clerk may use first class mail as the initial form of summons, incorporating any reasonable form of request for acknowledgement which is deemed practical and which would provide a reliable proof of service. One permissible method is the use of a duplex card properly addressed to the person summoned to be a juror and requesting the person so summoned to detach and return to the issuing clerk the part of the duplex card which is attached for his acknowledgement with his signature thereon. As used in this Section, a "duplex card" means any postcard with 2 mailable parts with a summons on one part and a detachable acknowledgement of receipt of such summons on the other part.
The issuing clerk may use certified mail as the initial means of service or as a secondary means of service in case the acknowledgement requested in a summons delivered by first class mail is not returned in the time period required. The certified mail may or may not be marked for delivery to the addressee only. The certificate of the issuing clerk that he has sent the summons in pursuance of this Section is evidence that he has done so. If the person summoned to be a juror does not return the acknowledgement of the summons in the time period requested, such prospective juror shall not be deemed guilty of contempt of court.
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 such fact is determined, re-issue such summons and deliver it to the sheriff of the county wherein the court is to be held, at least 10 days before the time of appearance hereinafter mentioned a summons commanding him to summon the person named therein so selected for the regular panel to appear before such court at or before the hour of 11:00 a. m. upon the date of appearance of the grand jurors established pursuant to Section 112-3 of the "Code of Criminal Procedure of 1963", approved August 14, 1963, as now and hereafter amended, to constitute a grand jury or at such time and date as the court may order for such re-issued summons. The sheriff shall serve such summons in the manner provided in Section 11 of this Act, for service of summons by the sheriff on petit jurors, and for any refusal or neglect so to do, shall be deemed guilty of contempt of court and may be fined therefor as provided in Section 11 of this Act, for default in summoning petit jurors. If for any reason the panel is not full at the opening of such court, the judge shall direct the sheriff to summon, at random, such number of persons named in the supplemental panel as the judge may determine to make available to fill the panel of grand jurors, and if the supplemental panel be exhausted without filling the grand jury panel, the judge shall select by lot from the jury list and direct the sheriff to summon a sufficient number of persons having the qualifications of jurors, as provided by this Act, to fill the panel; however, the court or judge may direct the clerk, at any time prior to the issuance of the summons for the regular panel, to include in the summons any specified number of the names listed on the supplemental panel, in the order in which they appear, starting with the first and counting consecutively, so that the persons so designated may be available in court for the filling of the grand jury panel, in which case the clerk shall also summon such supplemental panelist as is provided in this Section for service on regular panel selections. In counties having jury commissioners, the names of the persons to constitute the regular and supplemental panels shall be drawn in the manner provided for the drawing of names of persons to serve as petit jurors in such counties; the 16 names to provide the regular panel shall be first drawn, and thereupon 12 names for the supplemental panel shall be drawn and listed on that panel in the order in which they are drawn.
705 ILCS 305/9