Okla. Stat. tit. 70 § 135a
In each county having a population of not less than thirteen thousand (13,000) nor more than twenty thousand (20,000) according to the 1960 and each succeeding Federal Decennial Census and a valuation of not more than Twelve Million Dollars ($12,000,000.00) tangible properties, not including valuation of homestead exemptions allowed in any year, there is hereby created in the office of the county treasurer of each county, in addition to all other deputies authorized or provided by law, a deputy for school accounts, for whose salary the county shall be reimbursed out of the surplus revenues of the school districts heretofore served wholly at county expense and whose accounts and funds are kept by and under responsibility of the county treasurer, which reimbursement shall be in the manner hereinafter provided.
Okla. Stat. tit. 70, § 135a