The first constitution (written Plan of govt.) in America?

Answer 1

It depends upon what you think a constitution is.
To me a constitution represents a set principles or guidelines agreed to by a "constituency" of people to govern themselves by.
I believe this would fall under that definition.
I won't disagree with the others about the articles of confederation but there are earlier documents.

The Mayflower Compact

In the name of God, Amen. We whose names are underwritten, the loyal subjects of our dread Sovereign Lord King James by the grace of God, of Great Britain, France, and Ireland, king, defender of the faith, etc.

Having undertaken for the glory of God and advancement of the Christian faith and honor of our king and country, a voyage to plant the first colony in the northern parts of Virginia, do by these present solemnly and mutually in the presence of God, and one another, covenant and combine ourselves together into a civil body politic; for our better ordering and preservation and furtherance of the ends aforesaid, and by virtue hereof to enact, constitute, and frame such just and equal laws, ordinances, acts, constitutions, and offices, from time to time, as shall be thought most meet and convenient for the general good of the colony: unto which we promise all due submission and obedience. In witness whereof we have hereunder subscribed our names at Cape Cod the 11th of November, in the year of the reign of our Sovereign Lord King James of England, France, and Ireland the eighteenth and of Scotland the fifty-fourth. Anno Domini [the year of our Lord] 1620.

Good luck.

Answer 2

Articles of Confederation.

Answer 3

Articles of Confederation, 1781, probably.

Answer 4

The Articles of Confederation. Google can fill you in on it.

Answer 5

Articles of Confederation
even i know that