Westphalia is a city in Osage County, Missouri, United States. The population was 378 at the 2020 census. It is part of the Jefferson City, Missouri Metropolitan Statistical Area.

Osage County is a county in the central part of the U.S. state of Missouri. As of the 2020 census, the population was 13,274. Its county seat is Linn. The county was organized January 29, 1841, and named from the Osage River.