This study was launched to document and analyze supportive housing residents' use of public services prior to entering housing and afterwards, in order to determine the cost savings of supportive housing to other systems. The hypothesis of the study is that supportive housing reduces a person's usage of expensive, primarily public-funded services. The study tracks individuals' amount of service usage for 2 years before they entered supportive housing, comparing it to their usage of services 2 years after, as well as the change in types of services utilized over time. The study included supportive housing residents across Illinois living in developments that had been in operation for at least one year, and that served individuals who are homeless or at risk of homelessness, and individuals who have a mental illness and/or who are formerly incarcerated.