Settlers in the Willamette Valley voted at Champoeg to form a civil government, laying groundwork for U.S.-style institutions in Oregon Country during the era of U.S.–British joint occupancy.
The Organic Act (often called the Organic Laws) was adopted, formally creating the Provisional Government’s basic structure—an important step toward orderly settlement and land-claim administration before U.S. territorial jurisdiction.
The United States and Great Britain signed the Oregon Treaty, agreeing to divide Oregon Country largely along the 49th parallel and ending the Oregon boundary dispute that had shaped migration and diplomacy for decades.
The U.S. Senate approved the Oregon Treaty, clearing the way for implementation of the new boundary and accelerating U.S. governance and settlement south of the 49th parallel.
Cayuse attackers killed missionaries Marcus and Narcissa Whitman and others at Waiilatpu amid tensions intensified by a deadly measles epidemic. The event helped trigger the Cayuse War and increased federal attention to organizing the region.
The Oregon Territory was established by an act of Congress signed by President James K. Polk, extending formal U.S. territorial governance over a vast area including present-day Oregon, Washington, Idaho, and parts of Montana and Wyoming.
Congress enacted the Donation Land Claim Act to promote agricultural settlement by granting land to qualifying settlers in Oregon Territory, dramatically increasing migration and accelerating displacement pressures on Indigenous lands.
Congress organized Washington Territory north of the Columbia River (and north of the 46th parallel eastward), reshaping governance in the Pacific Northwest and reflecting rapid population growth and regional political demands.
At Point Elliott (Mukilteo), U.S. officials and several Puget Sound tribes signed a major treaty that created reservations and explicitly reserved tribal fishing rights—central to later legal and political conflicts in Washington Territory.
Following the Walla Walla Treaty Council, the Cayuse, Umatilla, and Walla Walla peoples concluded a treaty establishing the Umatilla Reservation and reserving rights to hunt, fish, and gather at usual and accustomed places—key terms that continue to matter legally.
After being drafted by a constitutional convention in 1857, Oregon Territory voters approved a state constitution—an essential step toward congressional admission and the transition from territorial to state government.
Congress admitted Oregon to the Union, bringing the territorial period to an end and formalizing U.S. state governance in the southern Pacific Northwest as settlement and institutions expanded rapidly after 1846.
Oregon Treaty and Settlement of the Pacific Northwest (1846–1859)
