For the purpose of fixing salaries specified in §§ 15.2-1608.1, 15.2-1608.2, 15.2-1609.2, 15.2-1627.1, 15.2-1636.1, and 15.2-1636.2, the population of each county and city shall be according to the last preceding United States census. If the area of any city has, since the last preceding United States census, been increased by annexation, the population of such city, for such purposes, shall be the population thereof as shown by the last preceding United States census, plus the increase resulting from such annexation. Whenever it appears to the satisfaction of the Compensation Board that the population of any county or city has, since the last preceding United States census, increased so as to entitle such county or city to be placed in a higher salary bracket, such county or city shall be considered within such higher salary brackets.
Va. Code § 15.2-1636.11