Lead (Pb) isotopes have been widely used to delineate Pb pollutants in the environment. Here, we present, for the first time, a systematic analysis of Pb isotopes in coal fly ash derived from coals from the three major coal-producing basins in the United States. Fly ash samples from Powder River Basin coals have higher 206Pb/207Pb ratios (1.2271 ± 0.0086, n = 7) than Appalachian Basin fly ash (1.2173 ± 0.0060, n = 16), while Illinois Basin fly ash samples are much more variable (1.2270 ± 0.0140, n = 22). The Pb isotopic signature of fly ash is distinguishable from that of major anthropogenic Pb sources in the United States, including leaded gasoline and paint, as well as the Pb isotope ratios of naturally occurring sediments and soils. Lead isotopic analysis of sediments from Sutton Lake in North Carolina, where other indicators have identified the occurrence of fly ash solids from unmonitored coal ash spills, shows a well-defined mixing between the Pb of unimpacted sediments and that of Appalachian Basin fly ash. This result further validates the applicability of Pb isotopes as a new tracer for detecting the occurrence of coal fly ash in the environment.