The optimal relational experiences of infants and young children demand a cross-sector workforce informed by Infant and Early Childhood Mental Health (IECMH) principles and practices. A recent review by the Alliance for the Advancement of Infant Mental Health, Inc identified seven themes that help define “What makes an IECMH association strong?”: (1) Identity, (2) Cross-Systems Collaborations, (3) Sound Organizational Structure, (4) Competency-Informed Training, (5) Reflective Supervision Capacity, (6) Policy, and (7) Higher Education. The present paper documents the story of the Association of Infant Mental Health in Tennessee (AIMHiTN) and the role of the Endorsement for Culturally Sensitive, Relationship-Focused Practice Promoting IECMH in that growth across those seven themes with the additional themes of (8) Funding and, (9) Diversity, Equity, Inclusion, and Belonging. First, foundational literature is reviewed to summarize IECMH-informed workforce development. Next, AIMHiTN's story of workforce development is mapped onto the nine themes and challenges and lessons learned are summarized. The article aims to serve as a roadmap for other states, provinces, territories, or nations hoping to develop their own Association for Infant Mental Health (AIMH) as well as a guide for those with existing AIMHs for promoting continued growth and sustainability.