This study reports on 177 supportive housing residents around Illinois, comparing their use of publicly-funded services two years before entering supportive housing to two years after entry. Data were collected from Medicaid-reimbursed services, state mental health hospitals, substance use treatment, state prisons, and various county jails and hospitals. The study found an overall cost savings of over $850,000 in the two years after entry into supportive housing, a little over $2,400 per person annually. There was a drastic reduction in state prison, county jail, and state mental health hospital overnight stays. There was a shift from using expensive inpatient services before housing (nursing homes, inpatient care, state mental health hospitals) to less expensive outpatient services after entry into housing (outpatient medical and psychiatric care, case management). Supportive Housing in Illinois: A Wise Investment was researched and written by the Heartland Alliance Mid-America Institute on Poverty with support from the Illinois Supportive Housing Providers Association and the Corporation for Supportive Housing.