Newnan was adjutant general of Georgia from 1806 to 1817.[2] In June 1812 Newnan (with the rank of Colonel) led two dragoons and 250 infantry of the Georgia militia to join the Patriot War in Florida. The Patriot Army was a group of American adventurers, primarily from Georgia, that was attempting to seize Spanish Florida. Newnan led an expedition into the interior of Florida in September to find and punish Seminoles who had attacked the Americans in Florida. His force consisted of 117 men, only 78 of whom were from the Georgia militia (the others had refused to extend their short-term enlistments). Newnan's company unexpectedly encountered a band of Alachua Seminoles led by King Payne. The ensuing battle quickly became a stalemate, and Newnan's force was pinned down for nine days before withdrawing.[3] During the Creek War, Newnan commanded a group of Georgia Volunteers; he fought the British at the Battle of Fort Peter.
^LaCoe, Norm (1974). "The Alachua Frontier". In Opdyke, John B. (ed.). Alachua County: A Sesquicentennial Tribute. Gainesville, Florida: The Alachua County Historical Commission. p. 7.