After the American Revolutionary War established US sovereignty over the territory of the upper Midwest, the new federal government defined the Northwest Territory in 1787 which included the area of present-day Indiana. In 1800, Congress separated Ohio from the Northwest Territory, designating the rest of the land as the Indiana Territory. President Thomas Jefferson chose William Henry Harrison as the governor of the territory, and Vincennes was established as the future capital. After the Michigan Territory was separated and the Illinois Territory was formed, Indiana was reduced to its current size and geography. In late 1816, the Indiana Territory was admitted to the Union as a state, although much of its territory was still in dispute as to possession by Native Americans. The land containing Putnam County was brought into the possession and control of the United States by the Treaty of St. Mary's in 1818 (known as New Purchase).