CogKnoSys

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Physical

Lower Columbia Counties

Five counties on the lower Columbia River: Clark, Cowlitz and Skamania in Washington, and Multnomah and Columbia in Oregon.

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The idea

The Lower Columbia Counties are five counties along the lower Columbia River. Three of them, Clark, Cowlitz and Skamania, are in Washington, while Multnomah and Columbia are in Oregon. Clark County sits across the Columbia River from Portland, Oregon. Every county has a county seat, which is the city or town where its local government is based.

The five counties are very different in size. Multnomah County is the smallest county in Oregon by area, yet at the 2020 census it had 815,428 people, the most of any county in the state. That same year Clark County had 503,311 people, Cowlitz County had 110,730 and Columbia County had 52,589. Skamania County had only 12,036 people. The county seats are Portland, Vancouver, Kelso, St. Helens and Stevenson, though Cowlitz County's largest city is Longview rather than Kelso.

Their names tell stories. Clark County is named for William Clark of the Lewis and Clark Expedition. The name Cowlitz comes from a Cowlitz word, Cow-e-liske, which may mean "river of shifting sands." Multnomah County takes its name from a Chinookan word for the "lower river." Four of the five, Multnomah, Columbia, Clark and Skamania, belong to the Portland metropolitan area, while Cowlitz County forms its own metropolitan area around Longview.

Check yourself

Question 1 of 3

Which of the five counties is not part of the Portland metropolitan area?

Pick one. The first pick counts.

Composition

what it's made of

  • Clark County, Washington — Washington's southernmost county; its county seat and largest city is Vancouver.
  • Cowlitz County, Washington — Formed in April 1854; its county seat is Kelso and its largest city is Longview.
  • Skamania County, Washington — The smallest of the five by population at the 2020 census, with its county seat at Stevenson.
  • Multnomah County, Oregon — Oregon's smallest county by area but its most populous at the 2020 census, with Portland as its county seat.
  • Columbia County, Oregon — An Oregon county whose county seat is St. Helens.

Connection

how it relates

Under Lower Columbia Region

In place

  1. Vancouver, Washingtonstrength 70 of 100

    Vancouver is the county seat and largest city of Clark County.

  2. Portland, Oregonstrength 70 of 100

    Portland, the county seat of Multnomah County, was the most populous city in Oregon at the 2020 census.

  3. Kelso, Washingtonstrength 60 of 100

    Kelso is the county seat of Cowlitz County.

  4. St. Helens, Oregonstrength 60 of 100

    St. Helens is the county seat of Columbia County.

  5. Columbia Riverstrength 50 of 100

    The Columbia River lies between Clark County and Portland, Oregon.

Change

how and why it evolves

Past
Clark County was created on August 20, 1845, by the Provisional Government of Oregon as Vancouver District, and at first it covered the whole of the present-day state. Cowlitz County was formed in April 1854, and Multnomah County's commissioners met for the first time on January 17, 1855.
Now
As of January 2026, Multnomah County had 574,215 registered voters, and in 2022 nearly 14,000 people moved from Portland to Clark County.
Next
Each new census will show how these counties change. The city counties and the rural ones may keep growing at different speeds.

Knowledge you can walk. Read the idea, then step up, across or down.

Lower Columbia Counties

Five counties on the lower Columbia River: Clark, Cowlitz and Skamania in Washington, and Multnomah and Columbia in Oregon.

Learn, discuss, create, buy or invest

The idea

The Lower Columbia Counties are five counties along the lower Columbia River. Three of them, Clark, Cowlitz and Skamania, are in Washington, while Multnomah and Columbia are in Oregon. Clark County sits across the Columbia River from Portland, Oregon. Every county has a county seat, which is the city or town where its local government is based.

The five counties are very different in size. Multnomah County is the smallest county in Oregon by area, yet at the 2020 census it had 815,428 people, the most of any county in the state. That same year Clark County had 503,311 people, Cowlitz County had 110,730 and Columbia County had 52,589. Skamania County had only 12,036 people. The county seats are Portland, Vancouver, Kelso, St. Helens and Stevenson, though Cowlitz County's largest city is Longview rather than Kelso.

Their names tell stories. Clark County is named for William Clark of the Lewis and Clark Expedition. The name Cowlitz comes from a Cowlitz word, Cow-e-liske, which may mean "river of shifting sands." Multnomah County takes its name from a Chinookan word for the "lower river." Four of the five, Multnomah, Columbia, Clark and Skamania, belong to the Portland metropolitan area, while Cowlitz County forms its own metropolitan area around Longview.

Check yourself

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