Abstract: How do White Americans operationalize Whiteness? This paper argues religion, in conjunction with country of origin, alters how self-identified White Americans assign ethnoracial labels to other groups. To test the role of religion on White assignment, this paper uses the case of Muslims and Middle Eastern and North African (MENA) Americans. Although MENA individuals are legally classified as White in the US, they are subjected to racialization and often conflated with Muslims. Using historical analysis of racial prerequisite court cases and a survey experiment, I find country of origin and religion play separate, additive roles in racial assignment decisions, both historically and today. White assignment is constructed of both country of origin and religion. These findings also extend to perceived skin tone. This is important because many of the benefits that come from being White depend on whether others perceive an individual as White. Understanding the constitutive parts of Whiteness compels research to be specific when discussing White people and why some “White” people are excluded.