The Massachusetts Constitutional Convention of 1820–1821 met in order to consider amendments to the Constitution of Massachusetts. It resulted in the adoption of the first nine amendments. Several other proposals were rejected.

Modernization and demographic changes put severe strain on the system set up in the 1780 constitution. New England was the epicenter of the American Industrial Revolution, and urbanization in mill towns and coastal ports led to cities several times larger than seen before in Massachusetts. Apportionment of the General Court was one of the biggest issues leading to calls for a convention. Under the old constitution all towns in Massachusetts were entitled to a representative, with the most populous towns entitled to a few extra representatives. The growth of larger urban towns like Boston caused greater dis-proportionality within this system, and the continual increase in the number of towns in the western part of the state meant the legislature had reached a large size. A smaller problem also occurred reapportioning the seats previously sent by Maine, which had been granted statehood in 1820. The convention sought to produce a more proportional legislature while reducing the size of the House and Senate.

The Constitutional Convention presented fourteen articles for the people's consideration:^[1][2]

Changed the constitutional support of public worship and appointment of public teachers to include all Christian denominations, not just Protestant. Provided that all church taxes raised in the State may go to the denomination of one's choosing, instead of only to the Congregational Church.

Also provided that no person may be imprisoned or brought to trial without an indictment by a Grand Jury.

To abolish support, by the towns, of protestant ministers and required attendance upon the instructions of the clergy

Choice	Votes	%
No	19,547	63.85
Yes	11,065	36.15
Total votes	30,612	100.00

Moved the start of the political year from the first Wednesday of May to the first Wednesday of January. All elected officials would start their yearly term starting on that date in January. The article also moved the date of the yearly state election to the second Monday of November from the first Monday of April.

To change the political year and date of state election

Choice	Votes	%
No	16,728	54.15
Yes	14,164	45.85
Total votes	30,892	100.00

Provided that if the General Court adjourned before the deadline the Governor had to return a rejected bill, then the law would not be passed.

To forbid bills unsigned after adjournment of General Court to become laws

Choice	Votes	%
Yes	17,949	63.63
No	10,709	37.37
Total votes	28,658	100.00

Allowed the state to establish city forms of government for towns over 12,000 inhabitants. It provided for the legislature to draft laws to allow these cities to have different forms of governance than the traditional town meeting.

To empower the legislature to grant city charters.

Choice	Votes	%
Yes	14,368	50.11
No	14,306	49.89
Total votes	28,674	100.00

Reduced the number of the Senate from 40 members to 36.

It also changed the apportionment for the House of Representatives. Under the article all towns over 1,200 people would be entitled to one representative, with an additional representative given for every 2,400 residents. All towns under 1,200 residents could choose to either be grouped with a second town to annually elect a representative, or choose to remain separate and elect a representative biennially and only be represented every other year. The article also capped the House's size to 275 members and allowed the legislature to raise the number of residents per representative every 10 years to compensate for population growth.

Provided the House to be paid out from the treasury, and set their quorum to 100 members. All members of the General Court were exempt from arrest when performing their duties as elected officials.

Reduced the number of members of the Governor's Council from nine to seven and set their quorum. It provided that the General Court shall elect them by joint ballot from among the people at large, instead of from the members of the legislature as it had been before.

To Change Method of electing Senators, Representatives, and Councillors

Choice	Votes	%
No	20,729	67.67
Yes	9,904	32.33
Total votes	30,633	100.00

Eliminated almost all property and tax restrictions for voting, the exception being paupers. All male citizens over 21 who had resided in the state for one year were entitled to vote.

Provided for the gubernatorial appointment of notaries public, the Commissary General, and vacancies for the Secretary and Treasurer.

Allowed men serving in the militia, but under the age of 21, to vote for their company Captains and Subalterns the same as men over the age of 21.

Amended the process of removing judicial officers, including justices of the peace.

Forbade the Governor and Legislature from soliciting the legal opinion of the Supreme Judicial Court.

Allowed the positions reserved for ministers of churches on the Harvard Board of Overseers to be open to all christian denominations. Harvard at the time was publicly funded and prior to this amendment it selected board members from the congregational church.

Amended the oath of allegiance required for all public officials to hold office. It provided an exception for Quakers who refuse to swear oaths.

Specified that no other oath or declaration was required to hold public office except for the one provided for in the eleventh article.

Forbade state judges from holding any other state office. Forbade anyone holding a state office from holding a federal office other than postmaster.

Changed the process for amending the Constitution. It required a vote of one-half of Senators and two-thirds of Representatives to vote positively on an amendment in two consecutive sessions. It would then be presented to the voters for approval.

The participants included:

Boston

• William Gray
• Isaac Parker
• Josiah Quincy
• Charles Jackson
• Peter Chardon Brooks^[3]

Dedham

• John Endicott^[4]

Saugus

• Jonathan Makepeace^[5]

• Worthington, Erastus (1896). "Report of the Curators". The Dedham Historical Register. Dedham Historical Society. Retrieved August 13, 2019.