Okla. Stat. tit. 19 § 901.20
Upon direction of the board, the clerk must compute and enter in respective columns of the assessment book the respective sums in dollars and cents in each fund to be paid on each piece of property therein enumerated and the clerk shall, no later than twenty (20) days after the valuations of the county have been certified by the State Board of Equalization, certify to the county treasurer in which such district is located the amount of assessment in each fund levied upon each tract by said board and the said county treasurer shall enter the amount of each in separate columns of the tax list of his county and the said assessments shall be collected by the county treasurer at the same time and in the same manner as all other taxes are collected in this state. If any such assessment becomes delinquent, then it shall draw interest as a penalty after delinquency at the rate of eighteen percent (18%) per annum. All such assessments and penalties collected or received by the county treasurer shall be paid by him to the treasurer of the district.
If any assessment shall remain unpaid for six (6) months after the same is due, the board of directors of the district may institute an action in the district court to foreclose the lien of such assessment and penalty and for a reasonable attorney's fees. All or any portion of the delinquent properties may be joined in one action. The summons shall be issued upon such petition as in other civil action and the cause tried by the district court. Judgment shall be entered for the amount of such unpaid assessment and penalty, and reasonable attorney fees, which judgment shall bear interest at the rate of six percent (6%) per annum. In the event that said judgment together with interest and costs and attorney fees is not paid within thirty (30) days from its date an order of sale shall issue by the clerk of said court directing the sheriff of said county to sell said real estate in manner and form as in case of the foreclosure of mortgages on real estate, without appraisement. Such sale shall be subject to existing taxes and special assessments. In the event that the board of directors of the district does not institute action to foreclose such delinquent assessment within one (1) year from the date the same is due, the holder of any bond or coupon issued under the provisions of this act may institute an action for and on the behalf of the district to foreclose the lien of such assessment and penalty. All such actions to foreclose shall be commenced within three (3) years from the maturity of the said assessment.
Okla. Stat. tit. 19, § 901.20