Formation of the Oregon Territory

Colorful map of the oregon territory showing the settlement routes and settler trails
The formation of the Oregon Territory led to more western settlement and helped catalyze The Pig War

Quick Facts
Oregon City, Oregon
First Capital of Oregon
On August 14, 1848 the United States congress approved the formation of the Oregon Territory. At the time the Oregon Territory included all of the present day states of Oregon, Washington, Idaho, and parts of Montana and Wyoming. Its capital city was located in Oregon City, not far from Portland. This vast, new territory had a sparse population of American settlers; two years later, the census of 1850 counted only 13,294 residents in the Oregon Territory.

The formation of Oregon came at a time of rapid expansion under the James Knox Polk administration, which centered Manifest Destiny and territorial growth in its domestic and foreign policy. On February 2, 1848, the United States and Mexico signed the Treaty of Guadalupe Hidalgo, which ended the Mexican-American War. With American military forces occupying Mexico City and much of their nation, Mexico surrendered all of the states of California, Nevada, Utah, most of Arizona, Colorado, and New Mexico, and some of Wyoming, Kansas, Oklahoma, and Texas (most of which had previously been conquered by Anglo-Americans). Two years earlier, the United States and Great Britain had signed the Oregon Border Treaty which guaranteed the US claims to the lands incorporated in the Oregon Territory. This same treaty had left the maritime boundary between the two nations inexact, leading eventually to the Pig War, but at the time the Northwest was so sparsely settled that it caused little international or local friction.

Four months later, in December of 1848, President Polk announced the discovery of gold in the newly conquered territory of California. Over the course of one year, California’s population increased more than 700 percent as 90,000 immigrants from around the world raced to the goldfields in this newly conquered territory. For residents of the Oregon Territory, including present day Washington, these new migrants provided an important and extremely valuable market for their agricultural and timber products.

Initially, the Oregon Territory suffered population losses due to the attractiveness of California gold, but the long-term population gains and prosperous markets that the gold rush created caused additional settlement in the Pacific Northwest. It also led to firmer federal control of these newly conquered lands and the violent displacement of indigenous communities. And eventually, these historical forces would lead to the Pig War conflict on San Juan Island.

Want to learn more about this period in history? Visit the McLoughlin House or Fort Vancouver which are operated by the National Park Service.

San Juan Island National Historical Park

Last updated: August 6, 2022