The Cambrian age Mt. Simon sandstone has been identified as one of the top storage reservoirs in the Midwestern United States for the permanent storage of carbon dioxide (CO₂) at commercial-scale volumes (50 million tons+). While the Mt. Simon sandstone has been the target of successful, large-scale injection tests in the Illinois Basin (>1 million tons CO₂ injected), in other regions, failed wastewater disposal wells and poor injection tests within the unit suggest poor injection potential. Because of these conflicting indicators, Mt. Simon sandstone reservoir quality is thought to be highly heterogeneous and may have negative impacts on CO₂ storage potential. In order to discern primary controls on overall storage potential, a geological database was developed to catalog the reservoir properties at ten selected sites across five states within three basins (Illinois, Michigan, and Appalachian) and the Arches province. Database components included information on lithology, facies, depositional environment, depth, thickness, porosity, permeability, structure, and diagenesis. The database also integrated data from cores and cuttings, mud logs, wireline logs, injection tests, brine disposal wells, and 3D static earth models along with previous regional studies. Updated regional maps of key properties were created including depth, thickness, average porosity, average permeability, and variance of reservoir properties. A geologic complexity ranking system was developed, tested, and applied to the various sites to rank them by reservoir quality, storage potential, and geologic complexity. The results show which regions have the greatest potential for storage and lowest risk for geologic uncertainty, and areas which have greater risks and lower storage. Additionally, the results show the influence of reservoir complexity on CO₂ storage. This methodology will be directly beneficial to the development of CO₂ storage programs and can be adapted for other energy storage uses.