Thomas R. Cornelius (November 16, 1827 – June 24, 1899) was a prominent American politician and soldier in the early history of Oregon. A native of Missouri, he moved to the Oregon Country with his family as a young man where he fought in the Cayuse War and Yakima Indian War against the Native Americans. He settled in Washington County near what later became Cornelius, named in his honor. A Whig and later a Republican, he served in the Oregon Territorial Legislature in the upper-chamber Council, and following statehood, he served in the Oregon State Senate. In the Senate he served one term as the president of that chamber and overall was in office from 1859 until 1876, except for one session. He also built the Cornelius Pass Road that bears his name. He was the father of Benjamin P. Cornelius, who was also prominent in state politics.