A considerable body of literature suggests that children's child-care experiences may impact adrenocortical functioning in early childhood. Yet emerging findings also suggest that the magnitude and sometimes the direction of child-care effects on development may be markedly different for children from higher risk contexts. Using data from a large population-based sample of families from predominantly low-income backgrounds in rural communities, we tested the degree to which links between children's child-care experiences (at 7-36 months) and their subsequent cortisol levels (at 48 months) were moderated by their level of cumulative environmental risk. Our results provided evidence of a crossover interaction between cumulative risk and child-care quantity. For children from low-risk contexts, greater weekly hours in child care were predictive of higher cortisol levels. In contrast, for children facing several cumulative risk factors, greater hours in child care per week were predictive of lower cortisol levels. These effects were robust after adjusting for several controls, including children's cortisol levels in early infancy. Child-care quality and type were not predictive of children's cortisol levels, and neither mitigated the conditional effect of child-care quantity on cortisol. These findings suggest that links between child care and children's development may differ as a function of children's broader ecologies.