Clatsop County is a county located in the U.S. state of Oregon. The county is named for the Clatsop tribe of Native Americans, who lived along the coast of the Pacific Ocean prior to European settlement. As of 2010, the population was 37,039. The county seat is Astoria.
The Lewis and Clark Expedition stayed for the winter of 1805-6 in the area of the future county at Fort Clatsop. Astoria, Oregon's oldest city, was established as a fur trading post in 1811 and named after John Jacob Astor.
Clatsop County was created from the northern and western portions of the original Twality District on June 22, 1844. Until the creation of Vancouver District five days later, Clatsop County extended north across the Columbia into present-day Washington. The Provisional and Territorial Legislatures further altered Clatsop County's boundaries in 1845 and 1853.
Before 1850 most of Clatsop County's government activity occurred in Lexington, a community located where Warrenton is now. However, commercial and social activities came to center on Astoria as that city grew, and an election in 1854 chose Astoria to be the new county seat.
Fort Stevens, located near the peninsula formed by the south shore of the Columbia river and the Pacific Ocean, became the only continental US military installation attacked in World War II, when submarine I-25 of the Imperial Japanese Navy fired 17 rounds at the base June 21, 1942. The submarine escaped when the order was given not to return fire with the shore guns. This was done to so that the base position was not given away. While the damage caused was slight (reportedly only a baseball backstop was damaged and a powerline severed), the presence of the enemy ship sowed panic along the Pacific coast of the United States.
In 1975, Clatsop County commissioners considered seceding from Oregon, and become a part of Washington. The movement was based on disagreements residents of the county had with then-Oregon Governor Bob Straub. The movement was created after Alumax Corporation changed their plans of building a plant in the county. Some residents, including two county commissioners, blamed the Oregon Governor for the movement of the plant. Then-Washington Governor Daniel J. Evans said the county was not welcome in the state of Washington. Clatsop County commissioners later abandoned the idea.