Or. Const. art. VI, § 10

The Legislative Assembly shall provide by law a method whereby the legal voters of any county, by majority vote of such voters voting thereon at any legally called election, may adopt, amend, revise or repeal a county charter. A county charter may provide for the exercise by the county of authority over matters of county concern. Local improvements shall be financed only by taxes, assessments or charges imposed on benefited property, unless otherwise provided by law or charter. A county charter shall prescribe the organization of the county government and shall provide directly, or by its authority, for the number, election or appointment, qualifications, tenure, compensation, powers and duties of such officers as the county deems necessary. Such officers shall among them exercise all the powers and perform all the duties, as distributed by the county charter or by its authority, now or hereafter, by the Constitution or laws of this state, granted to or imposed upon any county officer. Except as expressly provided by general law, a county charter shall not affect the selection, tenure, compensation, powers or duties prescribed by law for judges in their judicial capacity, for justices of the peace or for district attorneys. The initiative and referendum powers reserved to the people by this Constitution hereby are further reserved to the legal voters of every county relative to the adoption, amendment, revision or repeal of a county charter and to legislation passed by counties which have adopted such a charter; and no county shall require that referendum petitions be filed less than 90 days after the provisions of the charter or the legislation proposed for referral is adopted by the county governing body. To be circulated, referendum or initiative petitions shall set forth in full the charter or legislative provisions proposed for adoption or referral. Referendum petitions shall not be required to include a ballot title to be circulated. In a county a number of signatures of qualified voters equal to but not greater than four percent of the total number of all votes cast in the county for all candidates for Governor at the election at which a Governor was elected for a term of four years next preceding the filing of the petition shall be required for a petition to order a referendum on county legislation or a part thereof. A number of signatures equal to but not greater than six percent of the total number of votes cast in the county for all candidates for Governor at the election at which a Governor was elected for a term of four years next preceding the filing of the petition shall be required for a petition to propose an initiative ordinance. A number of signatures equal to but not greater than eight percent of the total number of votes cast in the county for all candidates for Governor at the election at which a Governor was elected for a term of four years next preceding the filing of the petition shall be required for a petition to propose a charter amendment.