St. Helens is the county seat of Columbia County, Oregon.The site of St. Helens was first known as Wyeth's Rock for the early trader, Nathaniel Wyeth, who had built a temporary post here in 1834 and was established as a river port on the Columbia River in the 1840s, and was the primary deep-water port, surpassing Portland until the destruction of the mail docks by fire. The docks burned down twice under mysterious circumstances, after which Portland became the primary port. St. Helens was incorporated as a city in 1889

Captain H. M. Knighton a native of New England took up the site as a donation land claim and in 1847 laid out the town as a competitor of the newly established Portland, which he contemptuously referred to as "Little Stump Town." It is said that Knighton named the town both to honor his native city of St. Helens, England, and for the beautiful mountain that rises a few miles to the northeast. According to some early records the vicinity was also referred to as Plymouth Rock or Plymouth and the earliest election district established here was named the Plymouth precinct. The earliest school was established in 1853 by the Reverend Thomas Condon, a noted scientist, who later became professor of geology at the University of Oregon. He added to his small salary as pastor of the St. Helens Congregational church by his teaching. The KNIGHTON HOUSE, 155 S. 4th St., was built in 1847 with lumber shipped around Cape Horn from Bath, Maine. Many of the town's buildings, including the COLUMBIA COUNTY COURT HOUSE, at First St. on the river bank, are built of stone from local quarries.