"Rural county" is defined in economic development statutes as a county with a population density of fewer than 100 persons per square mile or a county smaller than 225 square miles. The Office of Financial Management determines which Washington counties are rural and publishes the determination each year. As of April 1, 2023, 30 of Washington's 39 counties are rural counties: Adams, Asotin, Chelan, Clallam, Columbia, Cowlitz, Douglas, Ferry, Franklin, Garfield, Grant, Grays Harbor, Island, Jefferson, Kittitas, Klickitat, Lewis, Lincoln, Mason, Okanogan, Pacific, Pend Oreille, San Juan, Skagit, Skamania, Stevens, Wahkiakum, Walla Walla, Whitman, and Yakima.
"Rural county" is further defined for contracts and taxes. Regarding contracts, the definition addresses the award of contracts between the Department of Commerce and associate development associations; regarding taxes, the definition addresses local retail sales and use taxes. In both, a rural county is defined as a county with a population density of less than 100 persons per square mile or a county smaller than 225 square miles, as determined by the Office of Financial Management under a statute directing the Office of Financial Management to prepare population projections for counties that adopt a comprehensive plan under the Growth Management Act.
"Rural county" is also defined in the Department of Commerce statute addressing the low-income rehabilitation revolving loan program and grant program as an area of Washington defined as a non-entitlement area by the United States Department of Housing and Urban Development. Non-entitlement areas are cities with populations of less than 50,000, with some exceptions, and counties with populations of less than 200,000.
A "frontier county" is defined as a county with a population density of less than 50 persons per square mile. The population density will be determined by the Office of Financial Management and published each year.
A frontier county is also a rural county, and as such, a frontier county is eligible for all benefits, services, and programs available to a rural county, unless specifically excluded.