Okla. Stat. tit. 69 § 316
The Commission, on or before the first day of June of each year, shall certify to the Oklahoma Tax Commission the county road mileage of each county and the total county road mileage of the state as such mileage existed on the first day of January of such year. Such mileage shall be the computation of the existing road mileage for counties including any mileage represented by streets or roads in municipalities with a population of less than two thousand five hundred (2,500) and any other streets and roads in municipalities with a population of less than five thousand (5,000) that the county has agreed to construct, maintain, or repair. Any roads removed from the State Highway System by the Transportation Commission and returned to the county road system shall be added to the total county road mileage of the said county.
Okla. Stat. tit. 69, § 316