A legislative briefing titled “The Decarceration of Transition Age Youth with Intellectual/Developmental Disabilities and Mental Disorders: Responding to an Emerging Problem” was held on May 15, 2019 in Washington, D.C., as part of Mental Health Awareness Month. Speakers discussed the increasing numbers of transition age youth with intellectual/developmental disabilities (I/DD) and mental illness who have become incarcerated in our county and city jails, and the impact this has had, including from a family point of view. Potential solutions such as decarceration and diversion of these youth into community services; prevention of incarceration through better outreach and care coordination; and better use of home and community-based services were shared. Grand Challenge Executive Committee member Ron Manderscheid, PhD, executive director of the National Association of County Behavioral Health and Developmental Disability Directors, was a lead organizer of the event.