If your curious you can view plat maps that may tell you , Many of those one room and some of the larger 2 room school structures have been kept in use ( Southfork twp , Kanabec county MN uses a old one room sch as TWP hall , Many others were sold , another about 8 miles south east of me is used as a barn, ,Ive seen some converted into houses) I doubt that many are truly abandoned and that many were sold cheaply to someone even if all they did was till and plant right up with in a couple feet of the old school , like another twps school to my east, the owner there plants all the way around the building while it slowly is caving in , fair odds the owner will just burn it down some day or let it be used for training fire fighters, Your county govt center or even your twp clerk may have a plat map that you can view on hand on site (in offices) Keep in mind most of them were built before so called property tax system was created so eventually un used ones likely were sold off to get the land back on the property tax rolls.