This paper investigates religious unity and religious experimentation in (re)conceptualizing Iranian nationalism. I draw on ethnographic research conducted in Iran in 2016 and the United States in 2017 to examine how the state uses collective identity, place, and patriliny to shore up religious nationalist claims, and how its citizens abroad may distance themselves from conflations of decent and territory with religion. My research suggests a strong connection between patrilineal claims of descent and Shi’i religious authenticity in Iran. It assigns all citizens to the religious category of their father, and conversion from Shiism is discouraged and in some instances unlawful. The state uses shrines of the Prophet Mohammed’s descendants, which are Shi’a mausoleums and pilgrimage sites, as sites for the promotion and territorialization of religious nationalism. It traces lineages not to Cyrus the Great or another non-Islamic figure, but to the founding figure of its faith, an Arab belonging to a different national category. Interviewees suggested to me that some of the men honored by the shrines were not regarded as descendants of the Prophet prior to 1979. However, the Islamic Republic’s Hajj and Pilgrimage Organization creates documentation of enshrined men’s genealogies through lines of male ascendants culminating in the Prophet (through his daughters), and displays it at the shrine sites, in publications, and through various other media. These efforts reveal post-revolutionary Iranian religion and nationalism to be deeply intertwined in Iran. My 2017 research with Iranian-Americans suggests that once distanced from Iran, many Iranians wrestle personally with religion, and perhaps to a greater degree than members of other immigrant groups. Working with Iranians in two countries, I found territorialization tethered by patriliny in one place, and seemingly deliberate deterritorialization and disconnection from patrilineal religion in the other place. Far from their previous context of state-imposed religious nationalism, Iranian Americans demonstrate a high degree of experimentation with the role of religion in reconstructing their imagined national community. Many seem to relish being untethered from descent-based religion, and adhere to other faiths, atheism or secularized ethnic expression. I argue that the absence of state-promoted territorialized boundaries of inclusion and exclusion results in a reconceptualized religiosity and heteroglossic sense of nationhood.