Background: Workers supporting adults with intellectual disabilities experience significant stress in their essential role during COVID-19. The purpose of this study was to describe the experience of these workers and determine predictors of emotional distress. Methods: Eight hundred and thirty-eight workers supporting adults with intellectual disabilities completed an online survey about their work during COVID-19 and their mental health in July 2020. Results: One in four workers reported moderate to severe emotional distress. Being older and more experienced, having counselling services available through one's agency, and engaging in regular exercise or hobbies outside work were associated with less distress. Workers who reported increased stress in the workplace, stigma towards their families because of their job, personal fears about spreading COVID-19, and receipt of medications for mental health conditions or therapy reported greater distress. Conclusions: More attention is needed to address the mental health of workers supporting adults with intellectual disabilities as they continue their essential work during the pandemic.