- December 1, 1969, TriMet replaces Rose City Transit as the provider of mass transit service in Portland.
- December 4, 1850, The Oregonian, now the oldest continuously published newspaper on the West Coast, is founded.
- December 8, 1876, A. Luelling becomes the first mayor of the city of Hillsboro, located in the Tualatin Valley.
- December 12, 1893, former Congressman George K. Shiel dies after a breaking his neck in a fall.
- December 14, 1871, Oregon Senator George Henry Williams begins tenure as United States Attorney General.
- December 21, 1936, Oregon's first female governor, Barbara Roberts, is born in Corvallis.
- December 28, 1978, United Airlines Flight 173 crashed in Portland killing ten onboard the DC-8 aircraft.
- December 29, 1855, a fire destroyed the Territorial Capitol building.
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