Decatur County, Indiana: History
In 1787, the US defined the Northwest Territory 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 capital. After the Michigan Territory was separated and the Illinois Territory was formed, Indiana was reduced to its current size and geography. By December 1816 the Indiana Territory was admitted to the Union as a state.
Starting in 1794, Native American titles to Indiana lands were extinguished by usurpation, purchase, or war and treaty. The United States acquired land from the Native Americans in the 1809 treaty of Fort Wayne, and by the treaty of St. Mary's in 1818 considerably more territory became property of the government. This included the future Decatur County, which was authorized by the state legislature on December 12, 1821. No settler was allowed in the area until the government survey was completed in 1820.
The Decatur County governing structure was formed in 1822. The county was named for Commodore Stephen Decatur Jr., naval officer in the First and Second Barbary Wars, and in the War of 1812. Decatur was killed in a duel in 1820.