Introduction: Substance-use related emergencies are a serious public health concern that affects the lives of first responders and the community members they serve. In 2020, the Center for Behavioral Emergency and Addiction Research initiated an online substance use and mental health training program for first responders, adding courses over time. This study analyzed participant characteristics to provide data-driven recommendations for enhancing online training. Methods: Demographic, professional background, and course completion data were extracted from the program's web-based learning management system for all 14 published courses. Data from the courses was merged into a single file and analyzed using descriptive statistics. Differences in age and years of experience by course were assessed using the Chi-Squared Test and Cramér's V. Informative visualizations were created using Python and Tableau. Results: Participants completed 2,518 trainings. The Substance Use Disorder in the First Responder Workforce and Coping with Anxiety courses were the most popular and recruited a total of 897 and 337 participants, respectively. Participants varied in age, profession, and years of experience, with Emergency Medical Service/Paramedics accounting for 45.15% of participants and 34.55% of participants having > 15 years of experience. Conclusion: The online self-paced mental health and substance use education for first responders was well received and attracted different individuals depending on the course. Future work should focus on determining the rationale for participation or lack thereof and exploring how materials could be tailored to meet the needs of the various demographic and professional populations.