Indiana Territory. The mouth of the Great Miami River became the base for determining the border between Ohio and Indiana. Indiana Territory became an organized territory of the United States by an Act of Congress signed into law by President John Adams May 7, 1800, effective July 4, 1800. Indiana Territory included the modern states of Indiana, Illinois, Wisconsin and Michigan. It formerly had been part of the Northwest Territory, but as Ohio began the process of gaining statehood in 1800, Congress separated the area into two distinct territories. At that time, the boundary line between the new Indiana Territory and Ohio -- still officially known as the Territory Northwest of the Ohio River -- was formed by the Greenville Treaty Line (1795). It ran northeast from a point on the Ohio River opposite the mouth of the Kentucky River (at Carrollton, Ky.) to Fort Recovery in Ohio. Disregarded was a congressional committee recommendation "that the line of division shall commence at the mouth of the Great Miami River, and run due north until it strikes the dividing line between the United States and Canada." Three years later, when the state of Ohio was formed, Congress followed the 1800 recommendation and the new state's boundary line was set as a line due north from the mouth of the Great Miami.
Indiana Territory was on Butler County's western border from 1803 until 1816, when the state of Indiana was admitted as the 19th state Dec. 11, 1816. An Ohio Historical Society web site says William Henry Harrison served as the first governor of the Indiana Territory until 1812. OHS says "Harrison also worked as the superintendent for Indian affairs in the American Northwest. He convinced many Native Americans to relinquish millions of acres of land in the northwestern part of the United States, despite the fact that the United States guaranteed the Indians this land in the Treaty of Greenville.
"Not all tribes were willing to forsake their claims to the land. Chief among these people were the Shawnee Indians, led by Tecumseh and the Prophet, Tecumseh's brother. These two men worked together to form a confederation of all Indian tribes west of the Appalachian Mountains. Fearing that the Americans would not be able to defeat Tecumseh's confederation if he did not act quickly, Harrison marched against Tecumseh in late 1811. While Tecumseh was away seeking additional followers, Harrison attacked the Shawnees' major village, Prophetstown.
"Prophetstown was located at the junction of the Tippecanoe River and the Wabash River in modern-day Indiana. Nov. 11, 1811, at the Battle of Tippecanoe, the American army destroyed the village and also succeeded in breaking up the native alliance. Indiana became the 19th state of the United States of America Dec. 11, 1816." (See Northwest Territory, Northwest Ordinance, Land Ordinance of 1785, Kekionga, Fallen Timber, Treaty of Greenville, Greenville Treaty Line and the Gore)