Here are sawmills (hardwood and softwood-processing) of the eastern and southern U.S. Note the variation in spatial density of sawmills. Mill location data for each state ultimately come from state reporting agencies. These agencies sometimes have differing size thresholds. Hence, part of the observed variation in mill spatial densities across states is related to these varying thresholds.
Additional spatial variation is caused by the amount of available forest inventory, the landscape, and species. With respect to the latter, it might be that hardwood sawmills are smaller, on average, than sawmills that consume southern pine, so that a hardwood forested landscape supports more mills than a landscape of dominated by southern pine species. If this is true, then it could explain the high spatial density of sawmills in hardwood-rich Kentucky and Tennessee, relative to the sawmill spatial densities found in states along the Gulf of Mexico.