Part of Oklahoma (kind of) secedes from the United States

[Hydrae]

The Navajo land in northern Arizona is a separate entity.

https://en.wikipedia.org/wiki/Navajo_Nation#Government

I thought this was interesting:

The United States still asserts plenary power and thus requires the territory of the Navajo Nation to submit all proposed laws to the United States Secretary of the Interior for Secretarial Review, through the Bureau of Indian Affairs (BIA).

The US Supreme Court in United States v. Kagama (1889) affirmed that Congress has plenary power over all Indian tribes within United States borders, saying that "The power of the general government over these remnants of a race once powerful ... is necessary to their protection as well as to the safety of those among whom they dwell".[18] It noted that the tribes did not owe allegiance to the states within which their reservations were located.[19]

Most conflicts and controversies between the federal government of the United States and the Nation are settled by negotiations outlined in political agreements. The Navajo Nation Code comprises the rules and laws of the Navajo Nation as currently codified in the latest edition.