The American Community Survey (ACS) and the Puerto Rico Community Survey (PRCS) ask respondents aged 1 year and over whether they lived in the same residence 1 year ago. For people who lived in a different residence, the location of their previous residence is collected. The county-to-county migration flows were created from tabulations of the current county of residence crossed by county of residence 1 year ago.

County-to-county migration flows are available up to and including the release of the ACS 5-year 2016-2020 dataset. For more information, please see the ACS 5-year Migration Flows Break in Series notice.