Since the 2010 census, the fastest growing counties in Tennessee among counties of more than 10,000 people were all in Middle Tennessee. From 2010 to 2012, the counties where the biggest percentage gain in population were:

1. Montgomery: Up 7 percent to 172,341 residents

2. Williamson: Up 5.3 percent to 183,180 residents

3. Rutherford: Up 4.5 percent to 262,604 residents

4. Davidson: Up 3.4 percent to 648,295 residents

5. Sumner: Up 3.4 percent to 166,123 residents

Source: U.S. Bureau of Census