February 22: The Adams-Onis Treaty is signed between the United States and Spain, which includes Spain withdrawing its claim to the Pacific Northwest.
1821: The North West Company merges with the Hudson's Bay Company with the latter becoming the British authority in the region.
1824: Fort Vancouver in the present day Washington city of the same name becomes the Hudson's Bay Company's Columbia District headquarters.
1830s: Pioneers from the United States begin coming to Oregon via the Oregon Trail. Transportation improvements brought declines in wagon traffic on the trail in the 1850s and 1860s, but the trail continued to be in use as late as the 1890s.
Oregon City becomes the American capital of Oregon Country.
1844 - June 24: A law is enacted to limit settlement of African Americans in Oregon Country including them being lashed every six months. Portions of this law were repealed that December.
1845: Portland is founded. It would later become the state's largest city.
1846 - June 15: The Oregon Treaty between the United Kingdom and United States is signed, setting the boundary between the two nations occupying Oregon Country at the 49th parallel and placing present day Washington in Oregon Territory.
1945 - May 5: A Japanese balloon bomb explodes in Lake County, killing six. These were the only people on American soil whose deaths were attributed to an enemy balloon bomb explosion during World War II.
1972: A law goes into effect charging customers who purchase certain bottled products with the fee being refunded when the bottle is recycled.
1984 - August to October: Followers of Rajneesh who settled in Wasco Countyinfect 751 people after contaminating salad bars in The Dalles with Salmonella in an attempt to limit the number of people who vote in that year's election thus giving their candidates a better chance of winning. This was the first and remains the largest act of bioterrorism in the United States.