Five days later all of Clatsop County north of the Columbia River was used to create Vancouver County, in what is now Washington. The Provisional and Territorial Legislatures further defined Clatsop County’s boundaries in 1845 and 1853.
The county currently occupies an area of 873 square miles and is bordered on the west by the Pacific Ocean, on the north by the Columbia River, on the east by Columbia County, and on the south by Tillamook County. Clatsop County was named for the Clatsop Indians, one of many Chinook tribes living in Oregon.
In those earliest days Clatsop County was run from a town called Lexington, but Astoria gradually gained prominence and was officially chosen as the county seat in 1854 (Lexington no longer exists – it was absorbed by a town called Yellow Bank, which was then obsorbed by Warrenton).