Massachusetts General Laws Part III. Courts, Judicial Officers and Proceedings in Civil Cases (Ch. 211-262) Ch. 241, § 3

If a case is begun in a probate court and the land is within the jurisdiction of the probate court in 2 or more counties, the court in which proceedings are first begun shall retain jurisdiction thereof, which shall exclude the jurisdiction of probate courts of other counties; but this shall not prevent the probate court in any other county where a part of the common land lies, not included in the original petition, from making partition thereof.