Sylvester Pennoyer (July 6, 1831 - May 31, 1902) was a populist Democrat and served as Governor of Oregon (1886 - 1894) and as mayor of Portland, Oregon (1896 - 1898).

Pennoyer was born in Croton-on-Hudson, New York, and studied law at Harvard. After graduating, he moved to Oregon where he practiced law and ran local businesses. He was the petitioner in the Supreme Court case Pennoyer v. Neff which defined legal jursidiction over citizens in different cases.

As typical for that time, he acted in a stridently partisan manner while governor. He pointedly snubbed president Benjamin Harrison when Cleveland visited Oregon in 1891. He refused to use his resources to protect Chinese Americans when asked by Grover Cleveland's Secretary of State on May 3, 1893. He again refused to intervene at the request of Cleveland when a group of unemployed workers, part of "Coxey's Army", hijacked a train to travel east and join a mass march on Washington, DC.

|- style="text-align: center;" | width="30%" |Preceded by:
George P. Frank | width="40%" style="text-align: center;" |Mayor of Portland, Oregon
1896-1898 | width="30%" |Succeeded by:
William A. Storey