Okla. Stat. tit. 19 § 138.4
In counties subject to the provisions of Section 138.1a et seq. of this title, wherein the district judges have determined, in accordance with Section 138.3 of this title that the protection of the unfortunate and poverty-stricken defendants subject to criminal action in such county require the employment of a county indigent defender on a full-time basis, such person so appointed shall not engage in any practice of law except in the performance of the duties as county indigent defender, and shall receive a salary commensurate with the salary received by the district attorney in said district, payable monthly, from the court fund of such county, provided such salaries shall not apply to counties of less than three hundred thousand (300,000) population; provided that if additional assistance is required by the county indigent defender to properly fulfill the duties of the office, the indigent defender may authorize the employment of and appoint assistant defenders on a full-time or part-time basis, which assistants shall be under the same restrictions as to the practice of law as the county indigent defender of such county, and each shall receive a salary commensurate with the range of salaries of assistant district attorneys in their districts, payable monthly, out of the court fund of the county as determined by the county indigent defender.
Okla. Stat. tit. 19, § 138.4