<p>Do population changes in the institution of religion contribute to population changes in mental health? To answer this question, we used seven rounds of national trend data from the 2012–2023 <i>Chinese General Social Survey</i> (n = 24,150) to formally test whether population changes in religious involvement were associated with population changes in depressive symptoms among older adults in Mainland China. In terms of changes in religious involvement, we observed secularization or downward trends in (1) any religious belief, (2) affiliation with Buddhism, folk beliefs, Islam, and Christianity, and (3) religious participation. With respect to changes in depressive symptoms, our results suggested downward trends or population improvements from 2015 to 2021. Our most important finding is that trends in religious involvement were unrelated to trends in depressive symptoms. Because religious belief, religious affiliation, and religious participation were mostly unrelated to depressive symptoms in our analyses, adjusting for religious involvement had no substantive impact on trends in depressive symptoms. Although religious involvement and depressive symptoms are changing in the population of older Chinese adults, these fluctuations likely have little to do with each other. Ultimately, our analyses challenge the notion that population-level shifts in religious involvement exert any consistent effect on the depressive symptoms of older adults in Mainland China.</p>