Children and young people (CYP) within the Child Welfare System (CWS) often experience a range of trauma‐related difficulties. However, systematic use of evidence‐based measures to support mental health assessment and care planning appeared to be lacking within CWS in Singapore. This study evaluated the use of evidence‐based measures to inform care planning in out‐of‐home residential care in Singapore. Participants were 65 CYP in care. Measures consisted of the Child PTSD Symptom Scale for DSM‐5 (CPSS‐5), Assessment Checklist for Children (ACC) and Adolescents (ACA), Child Behavior Checklist (CBCL) and Youth Self‐Report (YSR). Care plans were identified based on the measures' clinical criteria and validated against the Child and Adolescent Needs and Strengths (CANS) and Adverse Childhood Experience (ACE) questionnaire. More intensive measurement‐based care plans were associated with higher service needs and lower strengths on the CANS, and higher ACE exposure. However, there was limited support for the validity of care plans when evaluated against the CANS and ACE questionnaire. Methodological implications for mental health assessment are discussed. Compared to service‐allocation‐as‐usual, measurement‐based care plans identified more cases that may require intensive psychological intervention. Overall, study findings provided some support for the use of assessment measures to supplement care planning in residential care.‘This study evaluated the use of evidence‐based measures to inform care planning in out‐of‐home residential care in Singapore’Key Practitioner Messages A comprehensive approach to care planning for CYP in out‐of‐home residential care should include the use of multi‐informant evidence‐based mental health assessment measures. The use of mental health assessment measures may reduce information gaps and complement the use of service needs assessment tools. Measurement‐based care planning may provide added value to supplement existing standard psychological care planning practices in out‐of‐home residential care.