The thermal regime of continental lithosphere plays a fundamental role in controlling the behavior of tectonic plates. In this work, we assess the thermal state of the North American upper mantle by combining shear-wave velocity models calculated using data from the EarthScope facility with empirically-derived anelasticity models and basalt thermobarometry. We estimate the depth to the thermal lithosphere-asthenosphere boundary (LAB), defined as the intersection of a geotherm with the 1300° C adiabat. Results show lithospheric thicknesses across the contiguous US vary between ~40 km and > 200 km. The thinnest thermal lithosphere is observed in the tectonically active western US and the thickest lithosphere in the mid-continent. By combining geotherm estimates with solidus curves for peridotite, we show that a pervasive partial melt zone is common within the western US upper mantle and that partial melt is absent in the eastern and central US without significant metasomatism.