We have tested the hypothesis that the lithosphere beneath the Williston Basin was heated, uplifted, and eroded prior to basin subsidence; this was accomplished by fission-track dating of apatite from samples of basement rock beneath and adjacent to the basin. Apatite fission-track ages of basement rocks beneath the basin range from about 4 Ma near the center to 554 Ma near the eastern edge. Combined with stratigraphic evidence, the ages suggest that at least 3 km of basement were eroded prior to subsidence of the Williston Basin. Rates of apparent uplift and erosion were on the order of 0.10 to 0.15 km/m.y. Apatite fission-track ages of basement outcrop samples on the eastern flank of the basin range from about 572 Ma to 441 Ma. These ages suggest that erosion of the flank occurred from the Early Cambrian to the Late Ordovician. We conclude that timing of uplift of the basement prior to subsidence of the Williston Basin is consistent with the thermal-origin hypothesis of basin formation.