Jefferson is a city in Marion County, Oregon, United States. It is part of the Salem Metropolitan Statistical Area. The population was 3,327 at the 2020 census. The city sits on the right bank of the Santiam River between Salem and Albany along Oregon Route 164 east of Interstate 5.

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.