Oregon Revised Statutes Education and Culture § 358.180

(1) When authorized by the electors as set forth in ORS 358.171, the county court may levy, in addition to the taxes now permitted by law to be levied, an ad valorem tax upon the taxable property in the county for the purpose of creating a county historical fund.

(2) The levy shall be a continuing levy in the amount required by the detailed estimates annually filed with the county court under ORS 358.200 less any amount carried forward from the preceding year excepting reserve funds previously set aside and approved by the county court, but not exceeding one-fortieth of one percent (0.00025) or such part thereof as is authorized by the electors of the county, of the real market value of all taxable property within the county, computed in accordance with ORS 308.207.