Francis Sylvester Monnett (March 19, 1857 – April 21, 1953) was Ohio Attorney General from 1896–1900 as a member of the Republican Party.

Under the administration of Monnette, the Ohio Attorney General's office pursued and won the first major victories that finally led to the permanent break-up of Standard Oil Trust established by John D.

While Monnett's term ended before the matter could be settled, the work done during his administration set the course for the final resolution.

Rockefeller funds were lavishly donated to Monnette's opponents, which led to his loss in the November 1900 election.

As a result of this probe, Ohio enacted the Valentine Act.