Tennessee Code Title 40. Criminal Procedure § 40-20-103

(a) In no case shall any person convicted of a felony be confined in the penitentiary for less than twelve (12) months. Whenever the minimum punishment is imprisonment in the penitentiary for one (1) year, but in the opinion of the jury the offense merits a lesser punishment, the jury may punish by confinement in the county jail or workhouse for any period less than twelve (12) months, except as otherwise provided.

(b) In counties of this state having a population in excess of six hundred thousand (600,000), according to the 1970 federal census or any subsequent federal census, in all cases where a person is convicted of a felony, misdemeanor or otherwise punished by confinement, the punishment by confinement will be served by imprisonment in a state penitentiary or county workhouse; provided, however, that in cases where trusty status is desired of the prisoner and is mutually agreed upon by both the sheriff of that county and the trial judge, sentence to the county jail would be allowed to the exclusion of any other statutory law or common law now in effect.