Mass. Gen. Laws ch. 147 § 8
County commissioners may appoint as police officers persons who are in the employment of the county, who shall, when on duty, wear in plain sight a metallic badge inscribed with the words "County Police" and the name of the county for which they are appointed. Such officers may preserve order in any court house or in any room or building used for county business and upon the adjoining premises. They may, without a warrant, arrest idle or disorderly persons who by their presence or conduct obstruct or annoy persons using county buildings or premises, or who violate section ninety-seven of chapter two hundred and sixty-six, and may take persons so arrested to the nearest police station or other place of lawful detention.
Mass. Gen. Laws ch. 147, § 8