Here in rural Canada usually they don't bother to tear down older buildings, they just let them return to the earth. In cities the government take the land and try to resell it. If nobody wants to buy it they tear it down. In farm areas there really aren't a lot of people to complain about vacant buildings. But like you said someone must own some of them as at the church the grass had been cut. I didn't go close to any buildings with cut grass as to me it feels like trespassing because obviously than some owner is making an effort to keep the place up. :-)