Numerous theories of religion rest on the assumption that the religious composition of local populations influences the religious identities of a person's close friends, but there have been few empirical tests of this assumption. Using a combination of data on the religious identity of close friends (from the 1988 and 1998 General Social Survey) and information on the religious composition of counties (from the U.S. Religious Congregations and Membership Study) we find that despite tendencies toward religious homogeneity, the religious composition of the surrounding population has an effect on the proportion of a respondent’s same-religion friends and on the proportion of friends belonging to specific other religious groups. Local population characteristics are unrelated to the proportion of respondents’ friends known in congregational settings. Results have implications for a broad range of sociological theories of religion as well as research examining the impact of same-congregation and same-religion friends (e.g., health and well-being).