Ongoing training and implementation support for mental health (MH) providers may help to bridge the often-noted research-to-practice gap in community MH care. However, MH providers typically have limited ability to access training or implementation support in evidence-based practices (EBPs). To address this need, the current study describes the reach and impact of a county-wide youth MH initiative aimed at increasing youths' and families' access to effective youth MH services by providing free EBP training and implementation support to MH service providers. Specifically, the initiative offered 1) formal workshops focused on specific EBPs, 2) a biweekly learning community, 3) individual case consultation or supervision, and 4) a confidential online session-bysession clinical feedback system. To evaluate the training initiative, we employed a mixed methods approach within a naturalistic, longitudinal design. Providers (N = 717) were asked to complete an initiatrainings and on a yearly basis thereafter (n = 255 completed at least one follow-up assessment). Measures included demographics, clinical practice information, self-reported confidence in treating youths with various problem types, organizational implementation climate, and EBP knowledge, attitudes, and practices. Additionally, we completed individual, semi-structured, qualitative interviews with a stratified purposeful sampling of providers (n = 13) based on level of participation in the training. While the training initiative had high reach, far fewer providers ultimately engaged in training. Results suggested providers who were trainees, who had higher baseline knowledge of EBPs, who used common evidence-based strategies more extensively, and who used other therapy strategies less extensively, engaged in more training. A provider's stage of career (i.e., being a pre-service trainee or post-graduate provider) consistently showed differences in training outcomes, with trainees haviEBPs, using common evidence-based strategies and other therapy strategies less extensively, and self-reporting less confidence in their effectiveness than post-graduate providers. Contrary to hypotheses, quantity and method of training were less consistently associated with change in training outcomes. Rapid qualitative analysis of semi-structured interviews complemented and expanded upon the quantitative results, illuminating provider, organizational, system, practical, and training activity-specific barriers and facilitators to training engagement and EBP implementation. Implications for future research and training initiatives are discussed in light of these findings.