Officially organized on February 14, 1845, the county was named for the then-disputed American territory of [[Oregon]], and is one of only three Missouri counties to share a name with another U.S. state (the others being Texas and [[Mississippi County, Missouri|Mississippi]]). [[Alton, Missouri|Alton]] is the county seat, and [[Thayer, Missouri|Thayer]] is the largest city. | Officially organized on February 14, 1845, the county was named for the then-disputed American territory of [[Oregon]], and is one of only three Missouri counties to share a name with another U.S. state (the others being Texas and [[Mississippi County, Missouri|Mississippi]]). [[Alton, Missouri|Alton]] is the county seat, and [[Thayer, Missouri|Thayer]] is the largest city. |