To complete and adopt the United States Constitution it had to be ratified by 9 of the 13 states of America.
Massachusetts was one of the states that opposed to sign the documents until people in charge reserve in the draft the right of undelegated power to the states and constitutional protection of political rights.
In February 1788 a deal was made and Massachusetts and other states compromised to sign. The ninth to sign was New Hampshire on June 21, 1788 and the Constitution begun on March 4, 1789.
George Washington was the first United States president and begun his presidential term on April 30, 1789.