Cornelius was born in
Missouri, on November 16, 1827, to Elizabeth and Benjamin Cornelius. In 1845, Thomas and his family traveled over the
Oregon Trail to the
Oregon Country and set up a farm on the
Tualatin Plains, north of what would become the community of Cornelius. The militia prosecuted the
Cayuse War in an attempt to punish those responsible for the killings at the
Whitman Mission. After
gold was discovered in
California, Cornelius journeyed there for a brief time, returning to the
Oregon Territory in 1849. The next year, he married Florentine Wilkes, and they had six children together before she died in 1864, including son
Benjamin. The family would settle on of their Donation Land Claim near Cornelius. In 1855, a second
war against the Native Americans started east of the Cascade Mountains against the
Yakama tribe. Cornelius volunteered again for the militia. For three months, he led a company with the rank of
captain before being elected as
colonel after
James W. Nesmith resigned his commission. Cornelius continued as colonel until the end of the war in 1856. During this campaign, his troops waged war indiscriminately against any natives found in the area. In one case, a Nez Perce native was accused of being a spy and summarily hanged, which alarmed members of the U.S. military. ==Political career==