Mass. Gen. Laws ch. 203E § 204
A trust shall be subject to the jurisdiction of the probate and family court department of the trial court of the commonwealth in the county where its principal place of administration is located. The principal place of administration of a testamentary trust shall be deemed to be the location of the court of the commonwealth in which the will creating the trust was granted informal or formal probate. Unless otherwise designated in the trust instrument, the principal place of administration of an inter vivos trust shall be the trustee's usual place of business where the records pertaining to the trust are kept or at the trustee's residence if the trustee has no such place of business. In the case of co-trustees, the principal place of administration, if not otherwise designated in the trust instrument, shall be: (1) the usual place of business of the corporate trustee if there is but 1 corporate co-trustee; (2) the usual place of business or residence of the individual trustee who is a professional fiduciary if there is but 1 such person and no corporate co-trustee; or (3) the usual place of business or residence of any of the co-trustees as agreed upon by them.
Mass. Gen. Laws ch. 203E, § 204