Individuals with severe mental illnesses (SMI) are a vulnerable population, struggling to cope with fragmented and often unwelcoming community service systems. Research has examined Assertive Community Treatment (ACT) as an intervention for SMI individuals, but little research has explored ACT’s potential as a community system change intervention. Using focus groups with ACT teams, we explored changes in community service systems as a result of ACT teams’ presence. Changes identified included increased understanding of SMI; increased access to services; and increased collaboration across service systems. Processes by which these changes occurred included knowledge communication, negotiation, renaming by association, and ongoing relationships.