Safety net benefits can help to improve the economic well-being of families with lower income levels, but many families and individuals who are eligible for benefits do not receive them. Designing the best interventions to increase participation rates requires knowing more about who receives assistance. We explored program participation rates in Illinois, focusing on seven programs: Temporary Assistance for Needy Families (TANF), Supplemental Security Income (SSI), the Supplemental Nutrition Assistance Program (SNAP), the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC), Public and Subsidized Housing, the Child Care and Development Fund (CCDF), and the Low Income Home Energy Assistance Program (LIHEAP). The analysis rests on detailed estimates of program eligibility produced by the Urban Institute's ATTIS (Analysis of Transfers, Taxes, and Income Security) microsimulation model. Statewide participation rates in 2018 varied from a low of 13 percent among families eligible for TANF to a high of 57 percent among those eligible for SNAP. Some subgroups of eligible families—for example, families with children with a single parent compared to those with two parents—are generally more likely to participate. Other patterns, including differences by race and ethnicity and by county population-size, vary across the programs.