Okla. Stat. tit. 18, § 592

The authority of persons associated together to become incorporated as a charitable corporation for the purpose of providing either a volunteer or full-time fire department for an unincorporated area or place is hereby ratified and confirmed. Such a corporate fire department shall have authority to provide fire protective service both to its members and to nonmembers, either within or without the unincorporated area wherein it is situated.