Project Summary/Abstract The COVID-19 pandemic has underscored the need for robust mental health services in the United States (US). In contrast, the mental health workforce is shrinking. Lack of resources has led to patients “boarding” for days in the Emergency Department (ED) while they await inpatient hospital beds. In attempt to address these issues, federal and state policymakers have recently enacted policies to improve the Nation’s mental health crisis care infrastructure. One such law changed the phone number for the National Suicide Prevention Lifeline (NSPL) to “988.” This simple number created an unprecedented demand for psychiatric crisis professionals who can respond to callers deemed to be at imminent risk of harm to themselves or others. The Substance Abuse and Mental Health Services Administration (SAMHSA) has put forth Mobile Crisis Units (MCUs) as a solution to this problem. MCUs are a psychiatric service that meets individuals in crisis wherever they are in the community to de-escalate, triage, and refer them to additional services. They represent a way to ensure NSPL callers can receive care in the least restrictive setting, thus preventing unnecessary hospitalization. According to the SAMSHA model, MCUs are two person teams composed of a mental health professional and a certified peer provider (i.e. a Certified Recovery Support Specialist [CRSS]). Many states must now significantly expand their mental health crisis workforce to effectively meet the needs of their citizens and follow SAMHSA’s recommendations. Illinois (IL) is an example of a state that has enacted policies designed to fill this gap. Two programs, the CRSS Success Program (CRSS-SP) and Program 590, were designed to increase the workforce of CRSSs able to work on MCUs and increase the number of MCUs in the state, respectively. These relatively new programs have yet to be evaluated on how effectively they are able to grow the state’s MCU workforce. Systems thinking is a framework that seeks to solve complex problems by understanding how parts of a system function to produce outcomes. Methods grounded in systems thinking, such as Group Model Building (GMB) and Simulation Modeling (SM), have a proven track record for effectively generating policies that solve healthcare workforce issues, but they have yet to be used in the context of the MCU workforce pipeline. The objectives of this study are therefore to 1) use GMB to create a map of Illinois’s MCU workforce pipeline system and evaluate if this method is effective in this context, 2) evaluate data from the CRSS-SP and Program 590 to determine which factors increase the likelihood that CRSSs and MHPs obtain and retain employment at MCUs, and 3) use SM to test policies that will help the state meet its MCU workforce needs. The recommendations generated by this study will be given to state government officials so they can be used to improve the lives of individuals in IL experiencing mental health crises.