Lewis Cass Building is a state government office in downtown Lansing, Michigan named for territorial governor Lewis Cass. It is Michigan's oldest standing office building, and served as the state office building until the completion of the first part of a new state government complex in 1953. The building is now a six-story U-shaped Classical Revival structure, a seventh story having been removed after a major fire in 1951. The building was added to the National Register of Historic Places as "State Office Building" in 1984.