The Sentencing Policy Advisory Council (SPAC) produces impact reports of proposed legislation that likely will impact the sentenced population. These statements provide policymakers with data, cost estimates, and projections for proposed legislative changes. With some exceptions, SPAC generally uses the same datasets and cost estimates across all analyses produced each year. This document summarizes the data, costs, and baseline projection that SPAC is using in our 2024 impacts reports. Please contact SPAC spac.general@illinois,gov with any questions about the data, costs, SPAC’s use of the costs, or projections.