In a given year, about 6 percent of the U.S. population picks up and changes counties. Young families move from Chicago to the surrounding suburbs. Recent college graduates cross the country for a first job in Boston, or Washington, D.C. Retirees relocate for good down to the Sunbelt.
If you could track all of these moves simultaneously across time, you'd get a picture of the parts of the country that are net population gainers, and those that are losing people instead. That picture would look like this:
On Thursday the Census Bureau released that map, alongside new data from the American Community Survey averaging county-to-county migration patterns over the five-year period from 2007 to 2011. In the above picture, dark blue counties lost the most migrants, even accounting for the people who moved in. Bright red counties – notably throughout Florida, the Southwest, and Colorado – gained more people than they lost, and often from all over the country.
This map just focused on Maricopa County, Arizona, one of those net migration hotspots, illustrates that people moved in and out from virtually the entire country:
Maricopa, home to Phoenix, lost more people to the blue counties, and gained more from the orange ones. In-migrants came from 957 separate counties, and out-migrants went to 1,190 of them, the largest number of any county in the U.S. What does that say about Maricopa? It's been both a magnet and a weigh station for people heading elsewhere.
The picture is strikingly different for Hennepin County, Minnesota, home to Minneapolis:
Or Philadelphia, which bears little migration connection to the entire Great Plains:
People meanwhile seem to be flocking to and fleeing from Los Angeles all throughout the country:
Alongside the new data, the Census Bureau updated its Census Flows Mapper tool here, where it's possible to zoom in on every county in the country, sorting migrants to and from that place by education and income level. In all, there are 3,221 counties in the U.S., including independent cities, boroughs and parishes that the Census Bureau counts in the same category. Add all of them together, and there are more then 10 million potential combinations of migration patterns between them. In reality, though, this ACS population sample yielded just 262,196 county pairs (no one moved between Maricopa and Sully County, South Dakota, for instance).
The resulting relationships between counties are as interesting as their individual status as net gainers or losers. People 25 and older with graduate degrees are predominantly headed to Los Angeles, Manhattan, Chicago, Middlesex County, Massachusetts (outside Boston) and Fairfax County, Virginia (outside Washington, D.C.). But migration flows were particularly large in between all of these counties, too.
Los Angeles, Miami, Detroit and Chicago also all lost a significant number of people who didn't travel very far – just to surrounding, suburban counties. Here we can see, for example, that Detroit has suffered a net loss of residents with college degrees to every one of its adjacent counties:
If you're a city interested in trying to keep these people, or in who else is luring them well, these maps are probably a good place to start.