fourth (adj.) Look up fourth at Dictionary.com
mid-15c., alteration, by influence of four, of ferthe, from Old English feorða; see four + -th (1). Compare Old Saxon fiortho, Old Norse fiorðe, Dutch vierde, Old High German fiordo, German vierte. In Quaker usage, which rejected the pagan weekday names, fourth day was Wednesday, often a secondary day of meeting for worship. The celebration of the Fourth of July as the epoch of American independence is attested from 1777.
That there is due to Daniel Smith, of the city tavern, for his bill of expences of Congress, on the 4 of July last, including a balance of an old account, the sum of 729 68/90 dollars; also a bill for materials, workmanship, &c furnished for the fire works on the 4 July, the sum of 102 69/90 dollars .... [Auditor General's report, Aug. 8, 1777, "Journals of Congress," vol. VII]