William Dunbar (1749-1810) was a Scottish-born American scientist and explorer. It was with Dunbar’s help that President Thomas Jefferson planned some of the first expeditions into the newly-purchased Louisiana Territory, including the 1804-05 Dunbar-Hunter expedition, which Dunbar led. Born in 1749 in Morayshire Scotland, Dunbar immigrated to Philadelphia in 1771. In the following years he traveled throughout the Deep South and Caribbean, while for the most part living in Spanish-controlled Louisiana. In 1783, with the Revolutionary War officially over, Dunbar relocated to United States territory, in present-day Mississippi. After his move, Dunbar established himself as a leading scientist in the region, and in 1800 Thomas Jefferson recommended him for membership in the American Philosophical Society.

In early 1803, months before the Louisiana Purchase, Jefferson wrote to Dunbar about his plans to secure “the whole left bank of the Mississippi (River) to a respectable breadth, and encourage a prompt settlement [of the region]"^[1] In the summer of 1804, the two began to discuss an expedition to explore either the Red or Arkansas River. Dunbar informed Jefferson that the Red River was “the most interesting of the two."^[2] After months of planning, the expedition set out on October 16, 1804. The expedition made its way through what is now northern Louisiana and southern Arkansas. Over the course of the trip, they were able to document the ecology of the region, always a topic of great interest to Jefferson. The expedition went as far north as the Ozark Mountains, which they briefly explored in December 1804. One of their most interesting findings was microorganisms living in the hot springs located in present day Hot Springs, Arkansas.^[3] After over three months of exploration, the group returned on January 26, 1805. Soon after returning, Dunbar wrote Jefferson a series of letters detailing some of the findings of the expedition. Jefferson gave his “acknowledgments” of the expedition and spoke of plans for future expeditions in the region, for which Congress had already allotted 5000 dollars.^[4]

In the years following the expedition, Dunbar continued his correspondence with Jefferson, and worked with him as an advisor for the Freeman-Custis Red River expedition. In addition, Dunbar wrote numerous scientific articles, many of which were published by the American Philosophical Society. Dunbar died at his Mississippi plantation, The Forest, in October of 1810.