Cognitive limitations affect 12% of midlife adults and are a risk factor for dementia in old age. Yet, the factors associated with the onset of cognitive impairment in midlife remain poorly understood. Guided by the cognitive reserve hypothesis which stipulates that having a spouse enhances cognitive well-being, we posited that persons who experienced marital dissolution through divorce or widowhood were at greater risk of cognitive impairment in midlife than their continuously married counterparts. Using data from the 1998-2014 Health and Retirement Study to estimate discrete-time event history models using logistic regression, we found that men who experienced widowhood during midlife had higher odds of cognitive impairment than those who remained married, and this differential persisted net of controls. For women, those who got divorced or became widowed faced higher odds of midlife cognitive impairment onset although these differentials were accounted for with the inclusion of controls in the full model.