Local people can act as sentinels for change, especially for wildlife populations not monitored by centralized governments. Responding to concern expressed by the Kitasoo Xai'xais (KX) First Nation over a decline in mountain goat (Oreamnos americanus) sightings, our community‐academic partnership assessed the conservation status of goats in KX territory and beyond in British Columbia by evaluating three independent information sources. Aerial surveys (2019 and 2020) over 542 km2 revealed a low‐density population (mean 0.25, SD 0.12 goats/km2), typical of peripheral coastal range. Interviews with KX Knowledge Holders revealed that sightings from sea level have declined sharply over 40 years, a period during which temperatures have increased and snowpack has decreased. Finally, Kill data (1980–2018) showed that kills/hunter/day initially increased among guided hunters before plateauing, but declined among resident hunters (~70% of hunt days) in both coastal and interior BC. Convergent patterns among datasets suggest that coastal goats declined in abundance and/or reduced use of low‐elevation habitat, disrupting a millennia‐old relationship between KX people and goats, thereby posing a conservation concern. Broadly, our work shows that detecting threats to peripheral populations, and wildlife in general, can be informed and empowered by the knowledge of place‐based peoples and associated decentralized management. Kitasoo Xai'xais First Nation mountain goat research illustrates roles of Indigenous peoples as sentinels of population and ecosystem change.