Abstract Background Cognitive problems associated with dementia affect a large proportion of older adults living in residential care. Knowledge of cognitive impairments is important for providing person-centred care (PCC). The impact of specific cognitive impairments on residents’ needs is often overlooked in dementia training and information about residents’ individual cognitive profiles are frequently underspecified in care-plans, potentially undermining the delivery of PCC. This can lead to reduced resident quality of life and increased distressed behaviours—a major cause of staff stress and burnout. The COG-D package was developed to fill this gap. Daisies provide a visual representation of a resident’s individual cognitive strengths and weaknesses in a colourful flower (Daisy) representing five cognitive domains. By viewing a resident’s Daisy, care-staff can flexibly adjust in-the-moment care-decisions and can consult Daisies in care-plans for longer-term planning. The primary aim of this study is to assess the feasibility of implementing the COG-D package in residential care homes for older adults. Methods/design This 24-month feasibility cluster randomized controlled trial involves a 6-month intervention of the use of Cognitive Daisies in 8–10 residential care homes for older adults after training of care staff on the use of Cognitive Daisies in daily care (basic training) and on conducting the COG-D assessments with residents (advanced training). The key feasibility outcomes include % residents recruited, % COG-D assessments completed, and % staff completing the training. Candidate outcome measures for residents and staff will be obtained at baseline, and at 6 and 9 months post-randomization. COG-D assessments of residents will be repeated 6 months after the first assessment. A process evaluation will assess intervention implementation and barriers and facilitators to this through care-plan audits, interviews and focus groups with staff, residents, and relatives. Feasibility outcomes will be analysed against progression criteria to a full trial. Discussion The results of this study will provide important information about the feasibility of using COG-D in care homes and will inform the design of a future large-scale cluster RCT to assess the effectiveness and cost-effectiveness of the COG-D intervention in care homes. Trial registration This trial was registered on 28/09/2022 (ISRCTN15208844) and is currently open to recruitment.