In the decline timeline, the Triforce is used by the monarchy (royal family) until the events of Zelda I, where it is split and distributed to Ganon, Link and Zelda.
In the child timeline, It is somehow split between those three (it is never explained how, just that it is) the triforce does not feature in FSA, which is the most recent game in the child timeline (chronologically speaking) so we don't know its exact state at this time.
As for the adult timeline, I haven't played PH or ST, so i'm not sure, but I believe the triforce of courage and wisdom are owned by Link and Zelda, but no mention of strength is ever seen (dun, dun, dun...) ThatsNotCanon 18:36, May 15, 2012 (UTC)
To elaborate on what is stated above, at the end of TP, the last Child game before FSA, Ganondorf loses the Triforce of Power, which is part of what finally kills him. At the end of WW (Adult), Ganondorf, who still has Power, kidnaps Zelda (Tetra) and holds her hostage in his tower, both as bait for Link and because she holds Wisdom. When Link, the bearer of Courage, arrives at the tower, Ganondorf attacks him and, with both Link and Zelda subdued, is able to take the Courage and Wisdom from them. Using the fully unified Triforce, he makes a wish that the Great Sea disappear so he can rule Hyrule, as he had always wanted. However, the King of Hyrule touches the Triforce first and asks the Golden Goddesses to destroy Hyrule once and for all and provide a future above the waves for Link and Zelda. Power, Wisdom, and Courage grant his wish, and the three pieces rise up and disappear, presumably going back up to the goddesses.
Here is my opinion on the matter (Spoilers):
- In the end of the Decline Timeline, at the end of Zelda II: The Adventure of Link. Link used the full Triforce to awaken Zelda the first. It isn't confirmed what happened to the Triforce, but it may have gone back to the heavens with the Goddesses, out of mortal reach.
- In the last game of the Child Timeline, Four Swords Adventure, the Triforce is not mentioned. But in the game before that, Twilight Princess, it does. At the end of the game, Ganondorf is defeated and killed, in which the Triforce of Power fades from his hand, it isn't known whether or not the Triforce of Wisdom and Courage fades from Zelda's and Link's hands. So it could either be that if the Triforce exists in the world still after this game, it is hidden.
- Neither of the games, Phantom Hourglass, nor Spirit Tracks mention the Triforce in the Adult Timeline. Wind Waker, the first game of the Adult Timeline, does however. At the end of this game, Daphnes Nohansen Hyrule makes a wish upon it, wishing for hope for the children Tetra/Zelda and Link, this wish eventually causes them to find a new continent, in which they name "New Hyrule", this land is also the setting of Spirit Tracks. After the wish is made, it floats up to the heavens, it isn't confirmed what actually happens to the Triforce afterwards, but I believe that it is sent to the Goddesses, away from mortal hands, much like my belief of what happens to the Triforce after Zelda II: Adventure of Link.
In short, it isn't confirmed at all of what befalls the Triforces at the end of each Timeline. Timelinesplitter 22:47, May 15, 2012 (UTC)
^Much like you said, at the end of The Wind Waker, after the king makes a whish, the Triforce goes back to the sacred realm, waiting for a new owner. I think the Triforce then remains permanently inaccessible as the only known bridge to the Sacred Realm, Hyrule, is sealed under the sea for good. ________________________________________