There is growing concern about the health of older US adults who live in rural areas, but little is known about how mortality has changed over time for low-income Medicare beneficiaries residing in rural areas compared with their urban counterparts. We evaluated whether all-cause mortality rates changed for rural and urban low-income Medicare beneficiaries dually enrolled in Medicaid, and we studied disparities between these groups. The study cohort included 11,737,006 unique dually enrolled Medicare beneficiaries. Between 2004 and 2017 all-cause mortality declined from 96.6 to 92.7 per 1,000 rural beneficiaries (relative percentage change: −4.0 percent). Among urban beneficiaries, declines in mortality were more pronounced (from 86.9 to 72.8 per 1,000 beneficiaries, a relative percentage change of −16.2 percent). The gap in mortality between rural and urban beneficiaries increased over time. Rural mortality rates were highest in East North Central states and increased modestly in West North Central states during the study period. Public health and policy efforts are urgently needed to improve the health of low-income older adults living in rural areas.