<p>Populations that are small and isolated are vulnerable to inbreeding and the loss of genetic diversity, which elevates their extinction risk. Southern greater gliders (<i>Petauroides volans</i>) are endangered Australian marsupials that have experienced substantial habitat loss and population declines across the species’ range. Genetic assessment and monitoring are critical for informing population-specific conservation management. In this study, we used conservation genomics to investigate an isolated, coastal population of southern greater gliders at Seven Mile Beach National Park, New South Wales, Australia. We analysed genome-wide SNP markers to evaluate population genomic diversity and structure and identify signs of possible temporal genetic decline. Reduced heterozygosity and elevated inbreeding were detected between 2020-21 and 2024. Population genetic structure was inferred by a significant pattern of isolation by distance. Spatial autocorrelation was positive at short distances (&lt; 300&#xa0;m), suggesting local genetic structure, but negative at longer distances (&gt; 2000&#xa0;m). A background level of relatedness and increased spatial proximity between close relatives was also observed, potentially contributing to a predisposition to inbreeding. Although no evidence of inbreeding depression was detected, the low effective population size estimate of 25.4 presents major concerns for population viability and instigates the need for urgent conservation actions. This study provides valuable insights into the impacts of isolation on southern greater glider population genomic diversity and structure. We report the first formal evidence of genetic decline within the population at Seven Mile Beach National Park and discuss how our genomic data can be used to inform conservation management.</p>