Although the Government of Indonesia has good data on forest cover and population, it does not have data on how many people live on state-claimed forest land. The objective of this study was to assess the extent of this deficiency and to develop a methodology for overcoming it, based on field research in the province of West Kalimantan. The project retrieved and combined government data on forests and people, analysed their significance in terms of numbers of forest-dwelling people, compared these results with government estimates and an empirical field-check, and sought to explain why knowledge of forest dwellers on state-forest lands is problematic. Results suggest that 20 to 30% of the population of West Kalimantan (approximately 650 000 to one million people) live on state-claimed forests. The main reason why it is difficult to determine how many people live on state-claimed forest lands is that a large number of villages remain unmapped and thus it is not possible to unite census data with forest boundaries in a spatially-precise manner. While the Indonesian Ministry of Forestry has not placed a high priority on determining how many people live on state-claimed forests, this study suggests that the lack of information on forest population densities is as much a consequence of the lack of information on village locations as it is a result of political or institutional interests.