The U.S. nonmetropolitan population peaked in 1940, when 75 million people, or 57 percent of all Americans, lived in small towns, in the open countryside, or on farms. Today, 46 million people representing just 14 percent of the 2020 population reside in nonmetropolitan areas. That rural people and communities have been “left behind” is a familiar but incomplete story.  We show that rural population decline between 1980 and 2020 reflects (1) the shift of rural counties to the metropolitan side of the demographic ledger, and (2) endogenous population decline in increasing numbers of nonmetropolitan counties “left behind” by urbanization. The demographic paradox is that rural decline encompasses many growing nonmetropolitan counties that are reclassified as metropolitan. This demographic winnowing process leaves behind those rural counties with the least potential for future growth. Our paper provides cautionary lessons—both substantive and methodological—regarding the commonplace narrative of widespread rural decline and urban growth.