Okla. Stat. tit. 19 § 450
For the purpose of determining whether such a vacancy exists the district court is hereby vested with exclusive jurisdiction and the district attorney of the county shall file a petition with the district court of the county where such vacancy is alleged to exist, and summons shall issue and be served in the manner provided by law for the service of summons in other cases, and said cause shall be tried to the court without the intervention of a jury and upon trial thereof, if it be shown by preponderance of the evidence that the county commissioner who is alleged to be incapacitated or disqualified is suffering from any mental or physical ailment that will prevent him from performing the duties of said office for the balance of the term to which he was elected, the said court shall enter judgment accordingly, decreeing that a vacancy exists, which judgment shall thereupon be final and the vacancy shall be filled as provided in Section 1 above.
Said action shall be brought by the district attorney and shall be in the name of the State of Oklahoma on relation of the district attorney as plaintiff, against the person who is alleged to be disqualified and the summons shall be issued, directed to the sheriff of the county where said defendant may be served, and if the said defendant be in a hospital or under the care or supervision of any institution, the same shall be served by delivering a copy thereof to the said defendant and a copy to the person or officer having supervision or control of the said hospital or institution and said cause shall stand for trial at the first non-jury docket setting after answer day, as other civil actions triable to the court.
Okla. Stat. tit. 19, § 450