Background: Monitoring population trends including mortality within subgroups such as people with intellectual and developmental disabilities and between countries provides crucial information about the population's health and insights into underlying health concerns and the need for and effectiveness of public health efforts. Methods: Data from both US state intellectual and developmental disabilities service system administrative data sets and de-identified state Medicaid claims were used to calculate average age at death and crude mortality rates. Results: Average age at death for people in state intellectual and developmental disabilities systems was 50.4-58.7 years and 61.2-63.0 years in Medicaid data, with a crude adult mortality rate of 15.2 per thousand. Conclusions: Age at death remains lower and mortality rates higher for people with intellectual and developmental disabilities. Improved case finding (e.g. medical claims) could provide more complete mortality patterns for the population with intellectual and developmental disabilities to inform the range of access and receipt of supportive and health-related interventions and preventive care.