W. Va. Code § 16-2-5

Any two or more counties or any county or counties and one or more municipalities within or partially within the county or counties may combine to create, establish and maintain a combined local board of health organized pursuant to and with the powers and duties prescribed by this article. The plan of combination must be approved by the commissioner. The service area of any combined local board of health is the combined territorial limits of the participating municipality or municipalities and county or counties: Provided, That if all or a portion of a participating municipality is located in a nonparticipating county, the service area of the combined local board of health is limited to the territorial limits of the municipality and does not extend to or include any area of the nonparticipating county outside of the municipal limits: Provided, however, That the service area of a combined local board does not extend to or include any area within the service area of a municipal board of health maintaining a separate full-time municipal health department under the supervision of a municipal local health officer.