BackgroundThe public health measures imposed in many countries to contain the spread of COVID-19 resulted in significant suspensions in the provision of support and care for people with dementia. The negative effects of these measures have been extensively reported. However, little is known about the specific impact on people with young onset, non-memory-led and inherited dementias. This group may have experienced different challenges compared to those with late onset dementia given their non-memory phenotypes and younger age. We explored the impact of the first COVID-19 lockdown on people living with familial Alzheimer’s disease, behavioural variant frontotemporal dementia, familial frontotemporal dementia, dementia with Lewy bodies, posterior cortical atrophy and primary progressive aphasia and their carers in the UK and their self-reported strategies for coping.MethodsThis was a mixed methods study. An online survey was administered to people with dementia and family carers recruited via Rare Dementia Support. Free-text responses were analysed using framework analysis to identify key issues and themes.Results184 carers and 24 people with dementia completed the survey. Overall, people with dementia experienced worsening of cognitive symptoms (70%), ability to do things (62%), well-being (57%) and changes to medication (26%) during lockdown. Carers reported a reduction in the support they received (55%) which impacted their own mental health negatively. Qualitative analysis of free-text responses shed light on how the disruption to routines, changes to roles and responsibilities, and widespread disconnection from friends, family and health and social care support varied according to phenotype. These impacts were exacerbated by a more general sense that precious time was being lost, given the progressive nature of dementia. Despite significant challenges, respondents demonstrated resilience and resourcefulness in reporting unexpected positives and strategies for adapting to confinement.ConclusionsThis study has highlighted the specific impacts of the COVID-19 restrictions on people with young onset, non-memory-led and inherited dementias, including behavioural variant frontotemporal dementia, primary progressive aphasia and posterior cortical atrophy, and their carers. The specific challenges faced according to diagnosis and the self-reported strategies speak to the importance of – and may inform the development of – tailored support for these underrepresented groups more generally.Visual abstractSupplementary InformationThe online version contains supplementary material available at 10.1186/s12877-023-03992-1.