From WoWWiki

This article contains lore taken from Warcraft II: Tides of Darkness, Warcraft II: Beyond the Dark Portal, the manuals, and official bonus maps.

Little is known of the island of Balor. It was domain of Azeroth lying west of Stormwind, it had been taken by the Horde during the First War and was held by the Stormreaver Clan during the Second War.^{W2Man 66} It is likely that it was liberated at the end of that war.

Balor does not appear on most recent maps and it is not currently accessible in the World of Warcraft. Balor was shown on early concept maps for World of Warcraft, so was at least in planning at one time.

Speculation

This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore!

Balor may not necessarily be the name of the island but the name of an outpost on an unnamed island, which is implied by the existence of the dot on the maps of Balor.

With Balor's connection to Stormreaver Clan, and its location near the Tomb of Sargeras, it may be part of the Broken Isles. In that case it would have been altered when Tomb rose from the sea floor. If it is part of the Broken Isles, its location is now closer to the Maelstrom. However, an early WoW concept map shows the tomb to be much further north of Balor as to make this scenario less likely.

Due to the moving of the Tomb of Sargeras out into the center of the Great Sea near the Maelstrom, it is possible that Balor (the island or the island it is located on) may have been moved as well. Its location is also similar to Hiji and/or Plunder Isle, and could have possibly been renamed when the islands of the south seas were later fleshed out.

With the knowledge that Balor was once a domain of Azeroth, its possible that its location would have to be moved somewhere closer to the regions of the Azeroth continent in game. One map of World of Warcraft shows some rather large islands west of the border between Stormwind and Westfall, that could possibly be candidates for Balor. Islands of that size do not show up near westfall in game.