Scholarship, including seminal research on prejudice, identifies adolescence as a critical period for the development of attitudes. Yet most sociological research on prejudice, especially in the form of anti-immigrant sentiment, focuses on the relationship between contemporaneous social conditions and attitudes towards out-groups while neglecting the demographic context during one’s impressionable years. Therefore, we design research to investigate the relationship among temporally distal and temporally proximal sub-national contexts and native-born attitudes towards immigration and immigrants. To do this, we merge geocoded data from the General Social Survey (1994–2016) with a unique US state-level dataset (1900–2015). Results from multilevel models reveal that immigrant presence during adolescence is a more consistent predictor of attitudes towards immigration and immigrants in adulthood. Thus, while the majority of sociological research on anti-immigrant sentiment asks if societal conditions matter, our results suggest that a more important question is when the context matters.