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.

Linn County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 128,610. The county seat is Albany. The county is named in the honor of Lewis F. Linn, a U.S. Senator from Missouri who advocated the American settlement of the Oregon Country. Linn County comprises the Albany, OR Metropolitan Statistical Area, which is included in the Portland-Vancouver-Salem, OR-WA Combined Statistical Area. It is located in the Willamette Valley. In 2010, the center of population of Oregon was located in Linn County, near the city of Lyons.