Provisional and Territorial Records Guide
Note: The following map is intended to provide researchers with a general understanding of significant county boundary changes over time. Researchers should refer to other sources for more detailed and precise representations.
Oregon was admitted as a U.S. territory on August 14, 1848. According to the 1849 census, there were 8903 white inhabitants of the territory. The Treaty with Great Britain in Regard to Limits Westward of the Rocky Mountains (1846), otherwise known as the U.S.-Great Britain Boundary Treaty of 1846, set the northern boundary of Oregon Territory at latitude 49'. The ten counties which now existed in Oregon still encompassed all of the area between latitudes 49' and 42' and west of the crest of the Rockies, an area of over 285,580 square miles.