Mass. Gen. Laws ch. 6, § 15BBBBB

The governor shall annually issue a proclamation setting apart the nineteenth of June as Juneteenth Independence Day, to be observed on June 19th of each year, in recognition of June 19, 1865 when Union General Gordon Granger announced freedom for all slaves in the Southwestern United States and in recognition of the end of slavery in the United States as well as the significant contributions, individuals of African decent have made to the commonwealth and to the United States and recommending that said day be observed in an appropriate manner by the people.