Local boards of health are county-level organizations in Washington, with a wide remit over matters of public health.  Boards enforce state public health statutes and rules through a Local Health Officer; enact and enforce local rules necessary to preserve, promote, and improve public health; supervise health and sanitary measures; control and prevent infectious diseases; prevent, control, or abate public health nuisances; and set certain fee schedules as authorized by the state Board of Health.

Each county has a local board of health that is coextensive with the county, unless the county has opted to create a health district on its own or in conjunction with one or more other counties.  A single-county health district operates in the same manner and has a similar governing structure to a local board of health.

The membership of a local board of health depends on whether the county it is in has adopted a home rule charter.  Noncharter counties operate under a commission form of government, with either three or five county commissioners.  All counties with fewer than 300,000 people have three commissioners.  Counties that have between 300,000 and 400,000 people may increase from three to five commissioners with voter approval.  Counties of more than 400,000 people have five commissioners. 
 
Counties that have adopted a home rule charter may instead adopt a form of county government other than the commission form.  Seven counties have adopted a home rule charter; four of these counties have adopted a county council with an elected county executive form of government, and three have adopted a commission or council with an appointed county administrator form of government. 

For a noncharter county, the board of health consists of the county commissioners and a number of other members equal to the number of commissioners.  The remaining members cannot be elected officials and must include representation from three different categories:  (1) health care providers, practitioners, or employees of health care facilities; (2) residents that are consumers of public health; and (3) other community stakeholders.  These members are selected by the county commissioners.  Unless the board of health demonstrates that it cannot find a member from one of the categories, all three of the categories must be represented on the board and membership from the categories must, if divisible by three, be divided evenly.  Additionally, if the county contains a federally recognized Indian tribe's reservation, trust lands, or usual and accustomed areas, or a charitable organization that serves American Indian or Alaska Native people and provides services within the county, then the board must include a tribal representative selected by the American Indian Health Commission.

The size of the board can be expanded to include additional members, including elected officials from cities and towns, as long as the number of members from the three categories is equal to the number of elected officials on the board.

The legislative authority of a charter county can determine the membership and selection process for the local health board in the county, but must include members from each of the three categories as evenly divided between the categories as possible, and the number of members from the three categories must be equal to the number of elected officials on the board.

In noncharter counties that have five county commissioners, the board of county commissioners may adopt an ordinance reducing the number of commissioners that serve on the local board of health, provided that at least one commissioner remains on the board.