Oregon’s Benton County was created by the Provisional Government of Oregon on December 23, 1847. At the time the county reached from the Willamette River south to the 42nd parallel (which now marks the border between Oregon and California), and west to the ocean. Polk County, from which Benton County was created, formed the northern border. Today Benton County is a much more manageable 679 square miles in the central Willamette Valley.
In 1851 Marysville, renamed Corvallis in 1853, was made the county seat.