1804 Treaty of Vincennes, which included the future Gibson County. Settlers had been pouring into the extreme SE part of the Indiana Territory starting in 1789, and by 1813 there was sufficient to form a local governing body. The area included in present-day Gibson County had been first placed under the jurisdiction of Knox County, formed in 1790. Parts of that extremely large county were partitioned off in 1801 to create Clark, in 1808 to create Harrison, in 1810 to create Jefferson and Wayne, and in 1811 to create Franklin counties. On 1 April 1813 the Territorial legislature authorized partitioning a further large section of Knox to create Gibson County. The boundaries of this new county were reduced that same month (30 April 1813) to create Warrick; in 1814 to create Perry and Posey; in 1816 to create Pike; and finally in 1818 to create Vanderburgh counties.