The U.S. Census Bureau has been releasing county-to-county and county/minor civil division (MCD)-to-county/MCD migration flow estimates based on the American Community Survey (ACS) since 2012. ¹ The first table package used 5-year ACS data collected from 2005 through 2009, the first ACS 5-year period.² For sequential 5-year ACS datasets, tables were crossed by selected characteristics for the period of 2006-2010 to 2011-2015 datasets. The 2008-2012 release was the first time flows from Puerto Rico municipios to U.S. counties were included. Flows between metropolitan statistical areas (MSAs) were introduced with the 2009-2013 dataset.³ In addition, the county-to-county flows going back to 2006-2010 dataset are available through the Census Flows Mapper.⁴ As of 2016, all ACS migration flows data for counties, MCDs, and MSAs were made available in the Census application programming interface (API) through the Census Developers site.⁵ This year’s migration flows table package (based on 5-year 2012-2016 ACS) will deviate from previous years in that it will not include socio-economic characteristics, only basic flow counts.