Background: Caring for someone with dementia can be physically and emotionally difficult. Acting as a caregiver can make it difficult to access sources of support, particularly in the later stages of dementia. This paper reports the development and presents the targets (subject areas) and components of a prototype website to support family caregivers of a person with dementia towards the end of life. Methods: Adopting an iterative approach and co-production methods the development process consisted of four stages: Stage1-Synthesis of data: Three sources of data (interviews, systematic review and theory) were synthesised using tabulation, to identify the targets of the prototype; Stage2-Identifying intervention targets and components: A research development group (health practitioners, a family caregiver and academic experts) met to discuss the development, using a modified nominal group process, refining the synthesis from stage 1; Stage3-Developing the intervention prototype: An outline of the prototype was developed based on stage 1 and 2; and Stage4-User testing: Interviews with caregivers testing the prototype website. Results: Qualitative interviews with caregivers identified four targets for the intervention: 1) feeling prepared and equipped; 2) feeling connected and supported; 3) valuing themselves as a caregiver and as an individual; 4) maintaining control of the caring situation and being the coordinator of care. The systematic review provided evidence on how and what components could address these targets, including providing information, peer support, contact with professionals, and psychological support. Theory helped to narrow the focus within each of these targets. Active discussion with the research development group and end users provided an outline of the prototype website. The prototype website presented addresses these targets with written information, videos from other caregivers, and peer and professional support sections. The subject areas covered included expectations at the end of life, support with day-to-day caring, care planning, and communication. Conclusions: This paper provides a detailed account of the development process of a prototype website for caregiver support. The transparent methodology and key lessons learnt from developing the prototype should help those who are developing similar interventions, across complex, progressive conditions and not just limited to dementia.