AbstractBackgroundIt is unclear whether the limitations of young persons with a mild intellectual disability or borderline intellectual functioning preclude feasibility of the daily diary method.MethodFor 60 consecutive days, 50 participants (M_age = 21.4, 56% male) who receive care in an ambulatory, residential, or juvenile detention setting, self‐rated both standardised and personalised diary questions through an app. Diary entries were used for feedback in treatment. Interviews were used to explore acceptability.ResultsAverage compliance was 70.4%, while 26% of participants dropped out. Compliance was good in ambulatory (88.9%) and residential care (75.6%), but not in the juvenile detention setting (19.4%). The content of self‐selected diary items varied widely. Participants deemed the method acceptable.ConclusionsDaily monitoring is feasible for individuals with a mild intellectual disability or borderline intellectual functioning receiving ambulatory or residential care, and can provide scientists and practitioners with important insights into day‐to‐day behavioural patterns.