The U.S. spends much more per person on the well-being of people with intellectual and developmental disabilities (IDD) compared to the general population, yet studies show that significant preventable health disparities persist. To address these disparities, systems must be able to identify and track experiences and outcomes in this population. The analysis outlined here demonstrates the ability to identify people with IDD in two health care data systems in Maine, the Maine Health Data Organization’s All-Payer Claims Database (MHDO APCD) and MHDO’s Hospital Encounter Database, by using MHDO’s de-identified person-index.