Oregon Constitution Art. IV § 3

(2)(a) If a vacancy occurs in the office of senator or representative from any county or district or subdistrict, the vacancy shall be filled as may be provided by law.

(b) Except as provided in paragraph (c) of this subsection, a person who is appointed to fill a vacancy in the office of senator or representative must be an inhabitant of the district the person is appointed to represent for at least one year next preceding the date of the appointment.

(c) For purposes of an appointment occurring during the period beginning on January 1 of the year a reapportionment becomes operative under section 6 of this Article, the person must have been an inhabitant of the district for one year next preceding the date of the appointment or from January 1 of the year the reapportionment becomes operative to the date of the appointment, whichever is less.