Oregon Revised Statutes Counties and County Officers § 204.020

(1) The term of office of each officer elected pursuant to ORS 204.005 commences on the first Monday of January next following election to office.

(2) Before entering upon any elective office listed in ORS 204.005, the person elected must qualify by filing with the county clerk of the county in which the person is elected the person's certificate of election, with an oath of office indorsed thereon, and subscribed by the elected person, to the effect that the person will support the Constitution of the United States and of this state, and faithfully carry out the office being assumed.  The person shall also give and file the undertaking provided for under subsection (3) of this section.

(3) A county governing body may require, by ordinance, for the filing by each officer under ORS 204.005, prior to that officer assuming office, of an official undertaking with such surety as the governing body determines necessary or of an irrevocable letter of credit issued by an insured institution, as defined in ORS 706.008, in either case in a reasonable amount with the county governing body.