Close kin provide many important functions as adults age, affecting health, financial well-being, and happiness. Those without kin report higher rates of loneliness and experience elevated risks of chronic illness and nursing facility placement. Historical racial differences and recent shifts in core demographic rates suggest that white and black older adults in the United States may have unequal availability of close kin and that this gap in availability will widen in the coming decades. Whereas prior work explores the changing composition and size of the childless population or those without spouses, here we consider the kinless population of older adults with no living close family members and how this burden is changing for different race and sex groups. Using demographic microsimulation and the United States Census Bureau's recent national projections of core demographic rates by race, we examine two definitions of kinlessness: those without a partner or living children, and those without a partner, children, siblings, or parents. Our results suggest dramatic growth in the size of the kinless population as well as increasing racial disparities in percentages kinless. These conclusions are driven by declines in marriage and are robust to different assumptions about the future trajectory of divorce rates or growth in nonmarital partnerships. Our findings draw attention to the potential expansion of older adult loneliness, which is increasingly considered a threat to population health, and the unequal burden kinlessness may place on black Americans.O lder adults without kin are some of the most disadvantaged and isolated members of society (1, 2), because close kin are vital sources of social support that affect social, economic, and physical well-being (3, 4). The availability of kin is repeatedly implicated in studies of healthy aging (5, 6), and lacking kin is among the social factors most positively associated with nursing facility placement and quality of care (7, 8). Loneliness appears to be increasing among older adults (9) and is more strongly associated with early mortality than smoking and excessive alcohol consumption (10). Because kin make up the dominant share of most Americans' close confidante networks (11), it is no surprise that loneliness is most prevalent among the never married, widowed, and divorced as well as the childless and those without partners (12, 13). Of course, not all close kin are in contact, geographically proximate, emotionally intimate, or willing or able to exchange resources, but the availability of kin is a necessary condition for their provision of such functions (14). For these reasons, it is important to examine the population dynamics of those who lack close kin (15). In the American kinship system (16), demographic events determine the availability of kin, with marriage and fertility producing kin and death and divorce reducing them. The clear links between demographic processes and kinship networks (17, 18) imply that ongoing demographic changes in American society ...