Mass. Gen. Laws ch. 1 § 3
Subject to such lateral boundaries as have been or shall be established between the commonwealth and adjacent coastal states, the territorial limits of the commonwealth shall extend seaward to the outer limits of the territorial sea of the United States. Such limits are without prejudice to the rights of the commonwealth in the seabed and subsoil of the continental shelf. The department of highways shall file, and may from time to time amend, a report with maps attached with the secretary of the commonwealth, and the exterior line of the commonwealth as located and defined therein shall be prima facie the marine boundary of the commonwealth.
The coastal baseline of the commonwealth, from which the breadth of the territorial sea is measured, shall be drawn in conformity with the treaties to which the United States is a party.
Nothing in this section shall change the limits of any fishing areas or any fishing rights which have been established under special acts.
The jurisdiction of the courts of the commonwealth over civil and criminal matters shall extend to all territory within the marine boundaries of the commonwealth, even though such territory may not be within any city, town or county. In such event, criminal and civil proceedings may be instituted in the courts of the county or judicial district closest to the place where the alleged offense occurred or cause of action arose, or in the superior court within and for the county of Plymouth or the third district court of Plymouth or in the superior court within and for the county of Essex or the first district court of Essex, to the same extent as if the alleged offense occurred or cause of action arose within said county or judicial district, any other jurisdictional or venue statute to the contrary notwithstanding.
The marine boundary of the commonwealth in the area of Rhode Island Sound south and west of the towns of Westport, Gosnold, and Aquinnah shall be and hereby is fixed as follows: from a coastal baseline beginning at the westernmost point of land, at mean low tide, in the town Aquinnah and running westerly to the easternmost point on the contour representing sixty feet of ocean depth above the formation identified as Brown's Ledge on Chart No. 1210 or its subsequent replacement published by the United States Coast and Geodetic Survey or by its successor, extending from said baseline to the outer limits of the territorial sea of the United States. In the event that a court of competent jurisdiction decrees that the coastal baseline shall run otherwise than herein described, the territorial limits of the commonwealth in Rhode Island Sound shall be measured from such other baseline. The ocean boundary with the state of Rhode Island shall be a line running from the most southerly point of the land boundary between the commonwealth and Rhode Island through the above-mentioned point on Brown's Ledge to the furthest limits of the territorial sea of the United States. The marine boundaries of the commonwealth in the area of Nantucket Sound shall be drawn to include the entire area of Nantucket Sound as territorial waters of the commonwealth.
Mass. Gen. Laws ch. 1, § 3