Section 725 ILCS 5/112-3 - Duration of Grand Jury(a) In counties with a population in excess of 1,000,000 a Grand Jury shall be convened, impaneled and sworn, and shall commence the performance of its duties for an indeterminate period, on the first Monday of each month. In such counties a Grand Jury shall serve until discharged by the court, except that no Grand Jury shall serve in excess of 18 months and not more than 6 Grand Juries shall sit at the same time. In counties with a population in excess of 225,000 but less than 1,000,000 a Grand Jury may be convened, empaneled, and sworn and may sit at such times and for such periods as the circuit court may order on its own motion or that of the State's Attorney. No Grand Jury shall serve in excess of 18 months and not more than 2 Grand Juries shall sit at the same time.
(b) In all other counties the Grand Jury shall be called and sit at such times and for such periods as the circuit court may order on its own motion or that of the State's Attorney; provided, that no Grand Jury shall sit for a period in excess of 18 months and, provided further, that no more than one Grand Jury shall sit at the same time.(c) At any time for cause shown the court may excuse a grand juror either temporarily or permanently and, if permanently, may impanel another person in place of the grand juror excused.