Forbes has created an interactive map that shows how many people moved to and from any given county in the United States in 2008. This is the map that's generated when you click on New York County (a.k.a. Manhattan), with black lines indicating various levels of incoming residents, and red lines indicating exiting ones. It's a fun little tool to play with, especially if you are from a small county in the middle of nowhere. Note that not enough people moved to the island from Wyoming, Montana, or the Dakotas to even register on the map, or vice versa. Of course, it should be noted, at least ten people have to have moved in 2008 to register on this map, and as we all know from Did You Hear About the Morgans?, they'd never allow that many New Yorkers to turn up in Wyoming.
Where Americans Are Moving [Forbes]