Abstract
The majority of undocumented immigrants to the United States enter through the southern border and most are from Mexico. Researchers in the US have been able to create estimates of how many unauthorised immigrants come from each country, but there has been little research on the geographical origins of immigrants from within Mexico. In this research we make use of a unique unduplicated file of people detained at or near the border by the US Border Patrol during the years 1999 to 2006. By focusing especially on the population aged 20–34, we are able to create a migration propensity index, which is the ratio of detainees from each state in Mexico to the population aged 20–34 in that state. The analysis of this index confirms the few other sources of information suggesting that migration from Mexico to the US is increasingly occurring from the more southern, indigenous states. A multiple regression analysis of the migration propensity index and state‐level variables finds that the death rate from accidents and violence among men aged 20–34 is the single most important predictor of a state's migration propensity index. This is related to a variety of factors indicating that migrants come from states with the poorest economic infrastructure. We discuss the implications of these shifts for both receiving and sending communities. Copyright © 2009 John Wiley & Sons, Ltd.