Source: United States Census Bureau
From press release:
The U.S. Census Bureau today released estimates from the American Community Survey showing how many people migrated from one specific county to another during the course of a year ─ the first such numbers published since these data were collected as part of the 2000 Census.
The American Community Survey compiles data over a five-year period and asks people where they lived one year prior to being surveyed. The first five-year estimates released covers the years from 2005 to 2009.
The 2005-2009 American Community Survey County-to-County Migration Files provide tables for each county in the nation, showing both “inflows” and “outflows.” Inflows are the number of people living in a given county who lived in another specific county one year earlier; outflows represent the number of people who lived in a particular county one year earlier who subsequently moved to another specific county.
Of the 48.1 million people who lived in a different residence in the United States one year earlier, 17.7 million lived in a different county.