Tennessee Code Title 67. Taxes and Licenses § 67-4-2907

(1) The county experienced a growth rate of twenty percent (20%) or more in total population from the 1990 federal census to the 2000 federal census, or the county experiences growth of twenty percent (20%) or more between any subsequent federal decennial censuses; or

(2) The county experienced a nine percent (9%) or more increase in population over the period from the year 2000 to 2004, or over a subsequent four-year period, according to United States census bureau population estimates.