Mass. Gen. Laws ch. 54 § 158
There shall be chosen by the voters of each of the counties, except Suffolk and Nantucket, at the biennial state election in nineteen hundred and forty, and in every fourth year thereafter, two county commissioners for said county, and at the biennial state election in nineteen hundred and forty-two, and in every fourth year thereafter, one county commissioner for said county, and in addition at each biennial state election such number of county commissioners as may be required to be chosen under section one hundred and forty-four to fill vacancies.
Not more than one of the county commissioners shall be chosen from the same city or town. If two persons residing in the same city or town shall appear to have been chosen to said offices, only the person receiving the larger number of votes shall be declared elected; but if they shall receive an equal number of votes, no person shall be declared elected. If a person residing in a city or town where a county commissioner who is to remain in office also resides, shall appear to have been chosen, he shall not be declared elected. If the person is not declared elected by reason of the above provisions, the person receiving the next highest number of votes for the office, and who resides in another city or town, shall be declared elected.
Mass. Gen. Laws ch. 54, § 158