When the Washington Territorial Legislature first met in March 1854, settler David Shelton represented Thurston County. To reach the capital and county seat in Olympia from his home on Hammersly Inlet, he had to paddle or row 20 miles. He and his fellow settlers wanted their own county to simplify filing land claims and other official business. He offered a bill to carve Sawamish County out of Thurston.
The first meetings of the interim county commissioners took place in the cabins of settlers Hugh Goldsborough and Michael Simmons. When settlers elected permanent county officers, the new commissioners chose the upper end of Oakland Bay as the county seat. Since there was no money for official buildings, the county seat was the cabin of whichever officer hosted meetings. The commissioners eventually learned that their site for a county seat had already been allocated for schools. They then placed the seat on the claim of William Morrow, which he called Oakland.
In 1864, the legislators changed the name to Mason County to honor the late secretary of state and acting governor, Charles H. Mason.
William Morrow was a Baptist minister and did not allow alcohol on his claim. David Shelton's claim, two miles down the beach, featured a floating saloon. Sheltonville or Shelton's Point had more population. In 1888, voters moved the county seat from Oakland to Shelton.