This study examines how housing and in-home supports affect public spending on individuals with chronic mental illness in Maricopa County, Arizona. It does so through a comparative analysis of average costs per person per year across three housing settings: permanent supportive housing, housing with unknown in-home support, and chronic homelessness. Specifically, it analyzes costs for housing, health care, and criminal justice during the period of 2014-2019. It also features a small-sample (small-N) case study of a housing setting that provides individualized, 24/7 in-home support to individuals with chronic mental illness (CMI) who have high support needs, examining average costs per person before and after moving into that setting (2016-2019). Finally, the study outlines recommendations from interviews with dozens of experts who work with and care for individuals with CMI in Maricopa County about reducing costs and improving care.