These files contain bilateral state-to-state migration flows constructed from the decennial US Census for 1960-2000. Starting with the 1940 Census, respondents were asked to provide their migrant status and their place of residence five years ago. The data in these files therefore indicate, for each pair of states (A,B), the number of respondents who lived in state A five years before and lived in state B at the time of the census.
Data provided by Youngjin Song, who used a more disaggregated version of this data in her job market paper.