W. Va. Const. art. VI, § 4

Division of state into senatorial districts. For the election of senators, the state shall be divided into twelve senatorial districts, which number shall not be diminished, but may be increased as hereinafter provided. Every district shall elect two senators, but, where the district is composed of more than one county, both shall not be chosen from the same county. The districts shall be compact, formed of contiguous territory, bounded by county lines, and, as nearly as practicable, equal in population, to be ascertained by the census of the United States. After every such census, the Legislature shall alter the senatorial districts, so far as may be necessary to make them conform to the foregoing provision.