Oakdale School, also known as Building 401, is a historic one-room school building located within Big Oaks National Wildlife Refuge (formerly Jefferson Proving Ground) in Monroe Township, Jefferson County, Indiana. It was built in 1869, and is a one-story, rectangular limestone building. It measures 24 feet wide and 30 feet deep, and has a front gable roof.

It was listed on the National Register of Historic Places in 1993.