Numerical modeling of geologic carbon sequestration (GCS) is needed to guide efficient development and to understand potential consequences of its development. The Illinois Basin is a major geologic basin in north-central United States. To evaluate the feasibility of future, commercial-scale GCS within this basin, a basin-scale, flow model is being developed using TOUGH2-MP/ECO2N and refined as new geologic data become available. Current models include the Mt. Simon Sandstone and its caprock (Eau Claire Shale). The project goals are to evaluate the migration of injected CO2 and assess the pressure changes in this open reservoir in response to future GCS developments.