Quincy, Omaha and Kansas City Railroad Office Building, also known as the O.K. Building and Sullivan County Courthouse, is a historic office building located at Milan, Sullivan County, Missouri. It was built in 1898 by the Quincy, Omaha and Kansas City Railroad. It is a two-story, rectangular brick building on a limestone foundation. It features a Romanesque style round arched entrance and second-story window openings. From 1908 to 1940, the building was used by Sullivan County as a courthouse and served as the seat of government for the county.
It was listed on the National Register of Historic Places in 1992.