Okla. Stat. tit. 82 § 549
Any time subsequent to the entry of the decree creating the district, and prior to the filing of the report of the board of appraisers, land situated outside of the district boundaries, necessary to accomplish the purposes of the district, may be included within the boundaries of said district. Said lands may be included within the boundaries of said district, by the filing, with the court having jurisdiction of said district, a petition, signed by owners of at least fifty-one percent (51%) of the land area and by not less than fifty-one percent (51%) of the landowners in the area proposed to be added to the said district. Proceedings of said petition shall conform to the proceedings to create a district as provided in this title. Upon said hearing, if the court finds that said land is reasonably necessary to be included within said district to accomplish the purposes for which said district was originally created, the court shall amend the boundaries of the district to include said land.
Any amendments to the boundaries of a district heretofore made by a court having jurisdiction thereof according to the procedure herein provided are hereby validated.
Okla. Stat. tit. 82, § 549