Race and ancestry are both popularly viewed in the United States as different but intertwined reflections on a person’s essentialized identity that answer the question of "who is what?" Despite this loose but well-understood connection between the two concepts and the availability of ancestry data on the U.S. census, researchers have rarely used the two sources of data in combination. In this article, drawing on theories of boundary formation, I compare these two forms of identification to explore the salience and social closure of racial boundaries. Specifically, I analyze race-reporting inconsistency and predict college completion at multiple levels of racial ancestry aggregation using Census data. The results suggest that, while much of the variation in these measures corresponds to popular "big race" conceptions of difference, considerable variation remains among individual ancestries.