The relation of community socioenvironmental characteristics to timing of the onset of decline of ischemic heart disease (IHD) mortality was investigated among the 507 State Economic Areas of the continental United States. Onset of decline was measured using data for White men aged 35-74 and classified as early (1968 or before) vs late (after 1968). Ten socioenvironmental characteristics derived from US Census Bureau data were strongly related to onset of decline. Areas with the poorest socioenvironmental conditions were two to 10 times more likely to experience late onset than those areas with the highest levels. We found that income-related characteristics could account for most of the difference in onset of decline of IHD between metropolitan and non-metropolitan places. We conclude that community socioenvironmental characteristics provide the context for changes in risk factors and medical care.