Many people living with dementia choose to remain in their own homes, supported by home-care workers, who provide care that is specified in care plans. We explored how care plans of clients living with dementia, compared with ethnographic observations of home care they received. In a secondary, reflexive thematic analysis, we reviewed care plans for 17 clients living with dementia and transcripts from 100 h of observations with 16 home-care workers delivering care to them. Our overarching theme was: Care plans as a starting point but incomplete repository. Clients’ care plans provided useful background information but did not reflect a wealth of knowledge home-care workers built through practice. Two sub-themes described: (a) Person-centred care planning: whether and how the care plan supported tailoring of care to clients’ needs and (b) Filling in the gaps: home-care workers often worked beyond the scope of vague, incomplete or out-of-date care plans. We found considerable inconsistencies between care plans and the care that was delivered. Care plans that were comprehensive about care needs, and rich in person-specific information aided the delivery of person-centred care. Lack of documentation was sometimes associated with observed failures in person-centred care, as helpful information and strategies were not shared. Including information in care plans about how, as well as what care tasks, should be completed, and frequently discussing and updating care plans can create more person-centred plans that reflect changing needs. Electronic care planning systems may support this.