Okla. Stat. tit. 82, § 82-614: Lands exempt and later liable to assessment

If any lands in any district organized under this act on which

benefits have been appraised and confirmed, are not liable for

assessment at the time of the execution of the work, but afterwards

during the period when such work is being paid for, become liable to

taxation or assessment by reason of some change in condition or

ownership, such lands shall thereupon be assessed as other lands in

said district receiving equal benefits. Providing that lands owned

by Indians, by the State of Oklahoma, or any political subdivision,

or any school district, shall be assessable under this act;

provided, however, districts established under this act are

authorized to enter into contracts providing for payment in lieu of

assessments on any such lands. Any assessments made on lands

previously exempt shall not be retroactive or cumulative, and such

lands shall be assessed, proportionate to the benefits appraised

thereon, for the remaining time required for payment of the cost of

such work.