First let me get this off my mind. If you ask what is the "largest state" everyone will assume by area but if you ask what is the "largest city" everyone will assume by population. Why?

But anyway the winner is:
Sitka, Alaska at 4812 sq mi (12,462 sq km).

The only problem is that there are no unincorporated areas in Alaska. If you look at real cities the winner is:
Oklahoma City at 612 sq mi (1609 sq km).

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