Whitman County, Washington: History
The area delineated by the future Washington state boundary began to be colonized at the start of the nineteenth century, both by Americans and Canadians. However, the majority of Canadian exploration and interest in the land was due to the fur trade, whereas American settlers were principally seeking land for agriculture and cattle raising. The Treaty of 1818 provided for dual control of this area by US and Canadian government officials. During this period, the future Washington Territory was divided into two administrative zones: Clark County and Lewis County (made official in 1845).
The dual-control concept was unwieldy and led to continual argument, and occasional conflict. The status of the Washington area was settled in 1846, when the Oregon Treaty ceded the land south of North latitude 49 degrees to American control.
In 1854, Skamania County was split from the original Clark County. Also in 1854, Walla Walla County was split from the new Skamania County. In 1863, Stevens County was split from Walla Walla County, and in 1871, a portion of Stevens County was set off to form Whitman County. The 1871 shape of Whitman County was considerably larger than its present boundary, as Adams, Franklin, and Lincoln counties were sectioned off from Whitman County in 1883. After that, Whitman County retained its shape, including through the period after Washington became the 42nd state of the Union in 1889.