This paper examines the health tradeoffs associated with the historical expansion in coalfired electricity generation in the United States. We combine newly digitized data on all major coal-fired power plants for the period 1938-1962 with two complementary difference-indifferences strategies. Coal-fired plants imposed large negative health externalities that were partially offset by the benefits from local electricity generation. The health impacts varied widely according to initial electricity access and evolved as the stock of generating capacity expanded over the sample period. These findings highlight the importance of accounting for both current and future payoffs when designing environmental regulation.