Objective: Informal caregivers of people with dementia develop their own beliefs about the condition, referred to as Dementia Representations (DRs), as they try to make sense of the changes they are observing. The first aim of this study was to provide a profile of the types of DRs held by caregivers. The second aim was to examine the impact of caregivers' DRs on their well-being, satisfaction with life (SwL) and caregiving stress. Methods: Participants were 1264 informal caregivers of people in the mild-to-moderate stages of dementia from time-point 1 of the IDEAL cohort study. Measures: DRs were measured using questionnaire items covering: Identity, Cause, Control, and Timeline. Results: Almost half (49.2%) of caregivers used a diagnostic term to describe the person's condition, although 93.4% of caregivers stated they were aware of the diagnosis. Higher well-being, SwL, and lower caregiving stress were associated with the use of an identity term relating to specific symptoms of dementia, attributing the cause to ageing or not knowing the cause, and believing the condition would stay the same. Lower well-being, SwL, and higher caregiving stress were associated with believing there was little that could be done to control the effects of the condition. Conclusion: Healthcare professionals should assess and gain an understanding of caregivers' DRs in order to provide more tailored information and support.