New figures from the Census Bureau show Chattanooga's population is now 11,000 behind that of Knoxville.
The Scenic City is less than 7,000 ahead of fast-growing Clarksville, which grew by 14,000 residents in just three years.
Nashville still leads with a population of 687,788. Memphis is next at 618,639.
Knoxville stands at 198,162, and Chattanooga comes in at 187,030.
Clarksville has risen to 180,716.
Murfreesboro is also in the top six, standing at 165,430. more