Forbes.com just published a handy tool today where folks can track population migration from county-to-county based on data the Internal Revenue Service collected from 2008.
Here's the migration pattern for St. Louis city:
The black lines show where people came to St. Louis from and the red lines show where they went to.
It looks like the highest concentration for moves was between the city and the county. It also appears that more people left than arrived, and most of the moves were to bigger cities, mostly on the East and West coasts. The largest population influxes came from Detroit and South Florida.
Here's the data for St. Louis County:
Which appears to have a similar pattern going on, only with more people. Exceptions: people moving to the county from the Gulf Coast, New York and Hawaii, but no Floridians.
Forbes offers no interpretation for these maps, which is really too bad. The reasons for some of the migrations are easy to guess -- in particular, the ones from Detroit -- but what's the connection between St. Louis and South Florida? Anybody want to venture a guess in the comments?