The stratigraphic horizon grids were generated by picking formation tops in 16,200 borehole geophysical logs and interpolating between them in the Williston Basin of North Dakota, South Dakota, and Montana. Collectively, the horizon grids outline the structural framework of the Williston Basin from the ground surface to the crystalline basement. The grids define the boundary surfaces between geologic layers in the 3D petroleum systems model. Not every horizon in the petroleum systems model, however, ties to a specific interpreted set of formation tops (see the ‘Williston_Basin_data_overview.csv’ table to see which horizons were derived from interpreted formation tops). Some horizons were split/calculated to accommodate source rock intervals or net evaporite thicknesses (denoted halite or anhydrite in the file name suffix). Although some lithostratigraphic units are not present throughout the entire area of interest (AOI), the petroleum systems model requires that each grid cover the entire AOI. Another requirement for the petroleum systems model is that each horizon grid be assigned a geologic age. This is a child item of a larger data release titled "Data release for the 3D petroleum systems model of the Williston Basin, USA".