"Rural county" is defined for economic development purposes 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 counties are rural counties.

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"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 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's population projections for counties that adopt a comprehensive plan under the Growth Management Act.
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"Rural county" is also defined for the Department of Commerce's low-income rehabilitation revolving loan program and grant program as a non-entitlement area defined 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 fewer than 50 persons per square mile. ?A "Frontier One" county has a population density of 21 or fewer persons per square mile.? A "Frontier Two" county has a population density of more than 21 but fewer 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.?