Tri-City is a census-designated place and unincorporated community in Douglas County, Oregon, United States. The population was 3,931 at the 2010 census. The community in Missouri Bottom near the Umpqua River is named for the three cities among which it is centered: Myrtle Creek, Canyonville and Riddle. The Tri City School District probably originated the name, which was later adopted by the local sewer district and the former Tri City State Airport.