Saltpeter (niter) is a naturally occurring nitrate mineral historically used to make gunpowder. Domestic production was economically viable only during times of international tension or conflict, when less expensive imports were curtailed. During the period leading up to the War of 1812, speculators and war preparations stimulated a saltpeter boom. Kentucky was the most significant source of nitrates, derived from caves and rock shelters, that supported regional gunpowder mills and was also shipped to eastern manufacturers. Prior research mainly concerned production from limestone caves; sandstone shelters received little notice. The only systematic survey of shelter sites was conducted by archaeologists for the Daniel Boone National Forest in eastern Kentucky, prompted by a need to assess prehistoric cultural resources. Examination of site inventory reports allowed identification of 165 shelter sites associated with saltpeter mining. This information, combined with primary historical documents, has allowed the authors to assess better the nature, distribution, and significance of this early Kentucky industry.