Oregon Revised Statutes Revenue and Taxation § 312.050

(1) On the day which is three months after the day of delinquency of taxes of the latest year, the tax collector, with the assistance of the district attorney, shall institute proceedings to foreclose the liens for all the delinquent taxes against each of the several properties included in the foreclosure list.

(2) One general proceeding shall be brought on the part of the county to foreclose the tax liens against each of the properties included in the foreclosure list. The person whose name appears in the latest tax roll as the owner of any property therein described shall be considered and treated as the owner of the property. Each such proceeding shall be a proceeding in rem against the property itself. If in any tax roll it appears that the owner of any property is unknown, or that the name of the owner is exempt from disclosure under ORS 191.501, then the property shall be proceeded against as belonging to an unknown owner.