Systematic differences of electoral participation between various social groups indicate crucial constraints of comprehensive democratic inclusion. Yet, there is a dearth of research on electoral participation among individuals with intellectual disability (ID), whose participation rates are considerably lower than among non-ID citizens. This study examines determinants of electoral participation among individuals with ID based on administrative records covering five cohorts of individuals from the Swedish upper-secondary school for pupils with ID (N = 8438), and their parents. Our main results indicate that the severity of the disability and parents who have voted are the strongest predictors of voting among individuals with ID. The latter suggests that family background is vital. However, the socioeconomic status of the families, such as parents' level of education, income, and occupation, are less pivotal factors.