Very useful and interesting MAP of TN inter-county migration using IRS data.
You have to click on both counties to see the net migration. For example, click on Davidson County and you will see that 12, 297 people moved from Rutherford County to Davidson. Then click on Rutherford and you will see that 24,628 people moved from Davidson to Rutherford County, i.e., Davidson County had a net outflow of 12,331 residents to Rutherford County.
This map was created for an interesting article in the Charlotte Observer about people moving from upstate New York to Charlotte.