We examine the size and composition of flows of Mexican migrants intending to cross the border and enter the United States. We focus on two characteristics which relate to eligibility for Social Security retirement benefits: legal immigration status and prior US migration history. We compare estimates from before and after the onset of the Great Recession in 2007. We analyze data from the Survey of Migration at the Northern Border of Mexico (EMIF-Norte), an innovative survey of migration flows fielded in border cities and towns in Mexico. We find that the declining overall level of migration from Mexico to the US since 2007 is driven entirely by declines in the level of undocumented immigration. The size of the legal immigrant flow from Mexico has actually increased since the recession began. We find an overall shift away from migrants with no previous trips to the US, toward migrants with 11 or more previous trips. There was no significant shift in the distribution of previous US trips among undocumented migrants, but among work-authorized migrants, the representation of both first time migrants and those with more than 11 previous US trips grew. The increasing share and absolute number of work-authorized Mexican immigrants with 11 or more past trips to the US seems likely to affect the share of Mexican immigrants qualifying for Social Security retirement benefits in the future, and it may be valuable to continue to examine these trends.