You can tell a lot about a place by who doesn't want to be there any more. Or, conversely, by who wants to move in.
A city that seeps population over time invariably has deeper problems driving its demographic change, like poor school districts that can't keep young families, or weak job prospects for its college grads. A county that attracts new residents, on the other hand -- maybe young people in particular, or retirees -- likely has the right amenities to lure them. Maybe a certain job sector. Or golf course communities.