Wash. Rev. Code § 8.08.010
Every county is hereby authorized and empowered to condemn land and property within the county for public use; whenever the board of county commissioners deems it necessary for county purposes to acquire such land, real estate, premises or other property, and is unable to agree with the owner or owners thereof for its purchase, it shall be the duty of the prosecuting attorney to present to the superior court of the county in which said land, real estate, premises, or other property so sought to be acquired or appropriated shall be situated, a petition in which the land, real estate, premises, or other property sought to be appropriated shall be described with reasonable certainty, and setting forth the name of each and every owner, encumbrancer, or other person or party interested in the same, or any part thereof, so far as the same can be ascertained from the public records, the object for which the land is sought to be appropriated, and praying that a jury be impaneled to ascertain and determine the compensation to be made in money to such owner or owners respectively, and to all tenants, encumbrancers, or others interested, for taking such lands, real estate, premises, or other property, or in case a jury be waived, as in other civil cases in courts of record, in the manner prescribed by law, then that the compensation to be made as aforesaid be ascertained or determined by the court or the judge thereof.
RCW 8.08.010