<p><b>BACKGROUND AND OBJECTIVES: </b>Although Hispanic/Latino populations in the United States are remarkably diverse in terms of birthplace and age at migration, we poorly understand how these factors are associated with cognitive aging. Our research seeks to operationalize a life course perspective of migration and health and contribute new understanding of Alzheimer's disease/Alzheimer's disease-related dementias among U.S.-based Hispanic/Latino older adults.</p><p><b>RESEARCH DESIGN AND METHODS: </b>Harnessing the Hispanic Community Health Study/Study of Latinos (n = 16,415) and the Study of Latinos-Investigation of Neurocognitive Aging (n = 6,377) data, we compare baseline cognition and 7-year cognitive change among U.S./mainland-born Hispanic/Latino adults relative to foreign/island-born immigrants by age of migration (4 groups: born in mainland United States, immigrated <16 years, 16-34 years, >34 years). Global cognition was calculated as a composite measure, and domain-specific measures were considered in secondary analyses. We employed linear regressions, ANOVA contrasts, and Blinder-Oaxaca decomposition techniques.</p><p><b>RESULTS: </b>All Hispanic/Latino immigrant adults, regardless of age at migration, have a cognitive health disadvantage (at each visit and over time) relative to U.S./mainland-born Hispanic/Latino individuals. Differences did not endure the inclusion of covariates and were explained predominantly by first socioeconomic and then acculturative factors, and far less by health and health behaviors. Acculturative factors are particularly important for individuals who migrated after childhood.</p><p><b>DISCUSSION AND IMPLICATIONS: </b>Socioeconomic and acculturation factors have outsized roles in explaining gaps in cognitive aging among U.S.-born and migrant Hispanic/Latino adults. It is then vital to examine whether disrupting socioeconomic and acculturation inequalities closes such gaps in cognitive aging.</p>