The mental health impacts of the COVID-19 pandemic on young adult carers have been neglected. This study aimed to identify COVID-19 related risk factors for young adult carers and to investigate their mental health relative to non-carer peers. Of the 1823 Italians aged 18–29 who completed an online survey, 1458 reported no ill family member (non-carers). Young adult carers included 268 with an ill parent, and 97 with an ill non-parent family member. Two mental health outcome categories were measured: COVID-19-related (risky health behaviors, loneliness, home violence, fear of COVID-19) and general (anxiety, depression, wellbeing). Six COVID-19 related risk factors were significantly correlated with poorer mental health in young adult carers. These factors constituted a COVID-19 Context Index. Compared to non-carers, young adult carers reported poorer mental health across all outcomes, as expected. The prediction that young adult carers caring for an ill parent would report poorer mental health than those caring for ill non-parent family members was evident only for the COVID-19-related mental health outcomes. The elevated rates of clinically significant distress and pandemic-related mental health problems among young adult carers highlight this group as a priority for mental health promotion interventions and whole-of-family support across multiple sectors.