In the documentary film, “Race the Power of an Illusion,” historian James Horton notes that “you could walk across a state line and literally, legally change race.” The comment refers to the different percentages that defined a person’s membership in the “Negro race” in Virginia, Florida, and Alabama, but it also points to the broader issue of how taxonomies of race vary locally within national contexts. This paper explores the question of racial variation as it applies to Arabic-speaking, primarily Syrian, migrants and their children in the US-Mexico borderlands in the early 20th century. Using census schedules, border crossing cards, directories, and other sources I analyze the ways in which Syrians moved in and out of racial categories: as whites, as Asians, as Mexicans, and as Arabs. The paper develops the concept of racial reassignation – a bureaucratic attempt to impose white supremacist categories of difference onto Arabic-speaking populations, particularly those whose lived experience cohered around hybrid, liminal, and mixed-race relationships.