Massachusetts General Laws Part IV. Crimes, Punishments and Proceedings in Criminal Cases (Ch. 263-280) Ch. 277, § 1

The clerk of the courts for each county, except Suffolk, Middlesex, Essex, Hampden, Norfolk, Plymouth and Worcester shall, not less than twenty-eight days before the commencement of the first sitting of the superior court for criminal business in each year, issue writs of venire facias for forty-five veniremen, from whose numbers the court shall select twenty-three grand jurors who shall serve in said court until the first regular sitting in the year next after they have been impanelled and until another grand jury has been impanelled in their stead. In counties where sittings of the court are established for the transaction of criminal business, they shall be required to attend only at such sittings.