William Wallace Thayer (July 15, 1827 – October 15, 1899), was an American Democratic politician active in U.S. states of Idaho and Oregon.

A mining boom in Idaho Territory caught Thayer's attention in 1860, prompting him to move west.

During the 1876 Hayes-Tilden Presidential Election dispute, Thayer was a member of the legal team which challenged the certification of J. W. Watts, a Republican elector for Rutherford B. Hayes.

Still appreciative of his assistance in the Watts Case, the Oregon State Democratic Party nominated Thayer for governor in 1878.

Thayer's time in office is remembered as a fiscally conservative, anti-corruption administration, which sought to make the state bureaucracy more efficient.

[citation needed] His lasting legacy was reforming the Supreme Court of Oregon into its present incarnation by statute.