This article builds on research on institutional language policies and practices, and on studies of the legitimization of racial categories in census data collection, in an exploration of language ideologies in the US Census. It traces the changes in language-related questions in the two centuries of decennial surveys, contextualizing them within a discussion of changing policies and patterns of immigration and nativism, as well as evolving hegemonic notions of race. It is argued that the US Census has historically used language as an index of race and as a means to racialize speakers of languages other than English, constructing them as essentially different and threatening to US cultural and national identity.