“Louisiana Purchases: The Indian Treaty System in the Missouri River Valley,1804-1859” combines traditional archival methods with GIS to examine the settler colonial transformation of the lower Missouri River Valley in the first half of the nineteenth century. The project’s digital components involve designing new visualizations of territorial conquest and demographic change in the trans-Mississippi West. One part of the project involves tying billions of dollars in expenditures flowing through the US-Indian treaty system and federal courts to a geodatabase of Indian land cessions in the region. The data, drawn from over a century of forensic accounting investigations compelled by Indian claims cases, enables the production of new visualizations of the acquisition of Indian country in the territory most commonly mapped as the Louisiana Purchase of 1803. Another component of the project includes the design of a suitability model that can be used to re-project federal census counts at the sub-county level, creating more accurate population distribution maps than those produced by the federal census bureau. These maps, in turn, allow me to demonstrate how the treaty system structured a series of population flood gates that turned projected dominion into practical sovereignty in the American West.