Mill City is a city in Linn and Marion counties in the U.S. state of Oregon on Oregon Route 22. The population was 1,971 at the 2020 census. It is on the North Santiam River, downstream from Detroit Lake.

Marion County is one of the 36 counties in the U.S. state of Oregon. The population was 345,920 at the 2020 census, making it the 5th most populous county in Oregon. The county seat is Salem, which is also the state capital of Oregon. The county was originally named the Champooick District, after Champoeg, a meeting place on the Willamette River. On September 3, 1849, the territorial legislature renamed it in honor of Francis Marion, a Continental Army general from South Carolina who served in the American Revolutionary War.