Mass. Gen. Laws ch. 78 § 10
A town which raises or appropriates money for the support of a free public library, or free public library and reading room, owned by the town, shall, unless the same has been acquired entirely or in part through some gift or bequest which contains other conditions or provisions for the election of its trustees, or for its care and management, which have been accepted by the town, elect by ballot at a meeting a board of trustees consisting of any number of persons, male or female, divisible by three, which the town determines to elect. When such board is first chosen, one third thereof shall be elected for one year, one third for two years and one third for three years, and thereafter one third shall be elected annually for a term of three years. The board shall, from its own number, annually choose a chairman and secretary and, if the town so votes, a treasurer, who shall give a bond similar to that given by the town treasurer, in an amount and with sureties to the satisfaction of the selectmen. Until the town otherwise directs the town treasurer shall act as treasurer of the board of trustees.
Mass. Gen. Laws ch. 78, § 10