Many people involved with the United States criminal legal system have experienced trauma, the long-term effects of which can challenge capacity to recover, often resulting in an increased risk of contact with the criminal legal system. Training programs can help professionals improve their understanding of trauma and implement trauma-informed responses. Limited research exists on the impact of trauma-informed response training for criminal legal professionals (e.g., corrections officers, court personnel, and law enforcement), and less is known about the effectiveness of the train-the-trainer (TTT) model in this context. In this article, we describe a four-phase, mixed-methods evaluation of a trauma-informed response training program delivered in the context of a 16-h TTT event to 28 criminal legal professionals in the southwest United States. We examine pre-and post-training knowledge acquisition, training experience, and impact on participant behaviors and attitudes 60 days post-training. Results provide preliminary support for the positive impact of traumainformed response training for criminal legal professionals. We discuss future directions for research on the effectiveness of trauma-informed response training for criminal legal professionals, including, critically, whether trauma-informed training contributes to improved outcomes for individuals involved with the criminal legal system.