Despite the overall consensus about the advantages of ecological momentary assessment, there is a need for information on how this method would fit with target groups with vulnerabilities that may potentially interfere with its feasibility. In this study, the feasibility of a daily diary protocol is therefore explored for adolescents and young adults with a mild intellectual disability or borderline intellectual functioning (MID-BIF). Once per day for 60 consecutive days, 50 participants with MID-BIF (Mage = 21.4, 56% male) from either an ambulatory, residential, or juvenile detention care setting, could self-rate a set of standardized and personalized diary questions through an app. Diary answers were channeled back to care professionals throughout the 60-day diary period, to be used as feedback in the participant’s treatment. A follow-up interview was conducted to explore the method’s acceptability among participants. The mean compliance rate was 70.4% and 26% participants dropped out. Compliance rates were good for participants who received ambulatory (88.9%) or residential care (75.6%), but not for participants who were detained in the juvenile detention center (19.4%). Participants who answered diaries on a group-owned device were significantly less compliant than those who could answer diaries on their own mobile phone. Interviews revealed that participants in all care settings deemed the method acceptable. Daily monitoring is a feasible and acceptable data collection method for individuals with MID-BIF who receive ambulatory or residential care, and can provide research and practice with important insights into day-to-day behavioral patterns.