Answer: New Brunswick, New Jersey, by order of George Washington
George Washington, July 3, 1778, It is ordered:
Tomorrow, the anniversary of the Declaration of Independence will be celebrated by the firing of thirteen Pieces of Cannon and a feu de joie of the whole line; the Army will be formed on the Brunswick side of the Rariton at five o'Clock in the afternoon on the ground pointed out by the Quarter Master General.
The Soldiers are to adorn their Hats wtih Green-Boughs and to make the best appearance possible...Double allowance of rum will be served out.
--The George Washington Papers at The Library of Congress
Come party like a founding father in the HOME of THE FOURTH of July! It started right here in New Brunswick. That's right, the first ever celebration of The Fourth of July happened by the direct order of George Washington, right here in New Brunswick! And they had drinks!!!
* A special thanks to Dorothea Berkhout for finding Washington's actual orders