In 1886, he was selected as sheriff of Crook County, serving in that office until 1888. In 1898, he returned to the House as a Republican during a special session of the legislature and returned for the 1899 session. Williamson was elected to the
Oregon State Senate in 1900 and served in the 1901 and 1903 sessions, but not the special session in 1903. Williamson represented Crook, Klamath, Lake and Wasco counties, and served as president
pro tempore of the Senate in 1901. In 1905, Williamson was convicted along with Oregon senator
John H. Mitchell and other co-conspirators on crimes involving political corruption and the illegal acquisition of public lands in the
Oregon land fraud scandal. The court remanded the case for a new trial, but no new trial occurred. ==Later years==