Okla. Stat. tit. 12 § 1193
Where the state is garnisheed, service shall be made by summons, as in other cases, upon the officer having control of the department or institution which caused the state to become indebted to the defendant in the case in which the garnishment summons is issued. Where the state department is under the control of a board or commission, service of the garnishment summons may be had upon either the chairman or the secretary of said board or commission. Service upon the officer having control of a state institution shall be had upon the president of the school, college or university, the superintendent of the institution, or the warden of the penitentiary or reformatory involved, although such persons may not be technically officers. It is the intent and purpose of this section that the officer, board or commission which caused the state to become indebted, and whose duty it is to see that the indebtedness is paid, shall be the agency of the state upon which the garnishment summons shall be served. Upon request of any such agency of the state, the State Treasurer shall draw warrants, or cancel warrants already drawn by him, and reissue same in such amounts as will enable the agency of the state served to comply with the garnishment proceedings. The State Treasurer shall not deliver any warrant direct to the payee thereof, but he shall in every instance deliver warrants drawn by him to the agency of the state which caused the indebtedness, to be paid by the warrant, to be incurred. Provided, that when a state officer not under the control of a state department or institution of the state is the defendant, service of garnishment shall be made by summons, as in other cases, upon the State Treasurer. Where the county is garnisheed, service shall be made by summons, as in other cases, upon the county clerk; where a city is garnisheed, service shall be made by summons, as in other cases, upon the city clerk; where towns are garnisheed, service shall be made by summons, as in other cases, upon the town clerk; where townships are garnisheed, service shall be made by summons, as in other cases, upon the township clerk; where township government has heretofore been abolished and the functions and powers of township government are being performed by a board of county commissioners, service herein shall be made by summons, as in other cases, upon the county clerk; where school boards or board of education are garnisheed, service herein shall be made by summons, as in other cases, upon the clerk of such boards.
Okla. Stat. tit. 12, § 1193