Cornelius is a city in Washington County, Oregon, United States. Located in the Portland metropolitan area, the city's population was 11,869 at the 2010 census. The city lies along Tualatin Valley Highway between Forest Grove to the west and Hillsboro to the east. Cornelius was incorporated in 1893 and is named for founder Thomas R. Cornelius.
In 1845, Benjamin Cornelius immigrated to Oregon with his family, traveling with Joseph Meek. The Cornelius family settled on the Tualatin Plains, near what is now North Plains. The same year, Benjamin Q. Tucker and Solomon Emerick staked land claims and established farms on the land that would eventually become Cornelius. At that time, the area was called Free Orchards; there was no actual community, but the name referred to the orchards on the 107 acres (0.43 km2) of land.
In 1871, Benjamin Cornelius's son Colonel Thomas R. Cornelius learned that Ben Holladay planned to extend the Oregon and California Railroad right through Free Orchards. Holladay had been told by Forest Grove and Hillsboro that they would not allow the railroad free right-of-way, so Holladay planned to bypass them, and build Free Orchards into a new city that would become the new county seat of Washington County.