Career
He helped build a ship that was sailed to California to exchange for cattle, and voted at the May 2, 1843, Champoeg Meeting. Armstrong immigrated to the in 1840. In 1842, he settled a farm in the Yamhill Valley, in what is now Yamhill County, Oregon.
During this time he helped build the Star of Oregon along with Felix Hathaway, John Canan, Ralph Kilbourne, Henry Woods, George Davis, Jacob Green, and later Joseph Gale.
The ship was then sailed to California where it was sold in a three-way deal where the Oregon pioneers received cattle. Armstrong and the others then drove 1,250 head of cattle, 600 horses and mules, and 3,000 sheep overland back to Oregon, arriving in early 1843.
On May 2, 1843, Pleasant Armstrong attended the meetings held at Champoeg, Oregon, where the pioneer settlers voted on whether to form a government. When troubles in Southern Oregon led to the Rogue River Wars, Armstrong volunteered.
On August 24, 1853, he was killed in action at Evans Creek in Jackson County.
His body was never recovered.