The causes of vacancies are set out in TCA § 8-48-101.  This section provides that any office in this state is vacated by the following:

1. Death of the incumbent;
    

2. Resignation, when permitted by law;
    

3. Ceasing to be a resident of the state, or of the district, circuit, or county for which he was elected or appointed;
    

4. Decision of a competent tribunal declaring the election or appointment void or the office vacant;
    

5. Act of the general assembly abridging the term of office, where it is not fixed by the constitution;
    

6. Sentence of the incumbent, by any competent tribunal in this or any other state, to the penitentiary, subject to restoration if the judgment is reversed, but not if the incumbent is pardoned; or
    

7. Adjudication of the incumbent's insanity.