Significance In the United States, 13% of households depend on an unregulated private well for their water. Compared with children in houses served by a regulated water utility, children in these homes have a 25% increased risk of elevated blood lead. Because lead is a neurotoxin, these children are at greater risk of experiencing irreversible cognitive damage, which can decrease their performance in school and increase their risks of behavioral problems. This study assesses associations between children’s blood lead and dependence on an unregulated private well for drinking water. It highlights the need for interventions to control lead corrosion from plumbing and well components (such as drop pipes, pump parts, and valves and fittings) in households depending on private wells.