In the extreme southern Missouri Ozarks, Oregon County was organized in 1845 and named for the Oregon Territory of the Far West. One of 11 counties along the Arkansas border, it lay in a region long roamed by various Indian tribes and claimed by the Osage until 1808. Charles Hatcher was probably the first settler in 1809, and early pioneers came largely from Kentucky and Tennessee, with a few from the East. The first county seat, Thomasville, was laid out on the Eleven Point River in 1845 on a site given by John and Matilda Thomas, but in 1859 the county seat was moved by law to a more central location and Alton was founded. During the Civil War, Union troops burned the courthouse there in 1863, and throughout the war the largely pro-Southern county suffered guerrilla raids and troop movements. A postwar outlaw band was routed by the county militia in 1868. Thayer, the county's largest town, was founded in 1881 as a railway division point on the newly built St. Louis, Fort Scott and Memphis Railroad, and early stations included Koshkonong, Saint Elmo, and American. Known for splendid scenery, the county is a lumbering and livestock farming area through which the spring-fed Eleven Point River runs in an arc, with hundreds of prehistoric Indian mounds found along it and its tributaries. In northeastern Oregon County and adjoining counties lay the historic Irish Wilderness, where Father John Hogan founded a Catholic colony in 1858; by 1859, forty families, many of them Irish, had settled there, and a colony chapel was built southeast of Wilderness village near the Ripley County line. Civil War activity ended that colony venture, and the area is now part of Clark National Forest, founded in the 1930s. Near Koshkonong lies Grand Gulf, an extensive chasm formed by a collapsed cave. The county's large springs, including Blue, Boze, Turner, Falling, Thomasson, and Greer, were all pioneer mill sites, and at Greer Spring, the third largest in the Ozarks, power was sent by cable from a turbine at the spring in the valley to the mill on the hilltop; Mammoth Spring, the second largest in the Ozarks, lies south of Thayer in Arkansas.