One of the distinguishing features of religious life in Western Europe in recent decades has been the sharp increase in the proportion of people who identify as unaffiliated with any religious tradition (religious nones). Non‐affiliation entails a rejection of religious belonging, not the absence of all religious belief and practice; yet the determinants of religiosity among nones have not been fully explored. Drawing on data from the 1998–2018 ISSP surveys in four West European countries (France, Germany, Great Britain, and Sweden), I test the impact of childhood religious socialization on the religiosity of unaffiliated adults by comparing lifelong nones, who were never religiously affiliated, with disaffiliates, who were raised within a religious tradition and have since exited organized religious life. Disaffiliates are consistently more religious than lifelong nones due to religious residue from childhood, with greater residue found among those who were more religiously committed as children. Religious decline among the unaffiliated over time, combined with the increasing proportion of lifelong nones and second‐generation lifelong nones who lack even an inherited, minimal religious residue, suggest that secularization will gather momentum.