Texas Tax Code - TAX § 151.309. Governmental Entities

(1) the United States;

(2) an unincorporated instrumentality of the United States;

(3) a corporation that is an agency or instrumentality of the United States and is wholly owned by the United States or by another corporation wholly owned by the United States;

(4) this state;

(5) a county, city, special district, or other political subdivision of this state;  or

(6) a state, or a governmental unit of a state that borders this state, but only to the extent that the other state or governmental unit exempts or does not impose a tax on similar sales of items to this state or a political subdivision of this state.