To start with, yes, it is an American basswood or Linden tree.  I searched to find out what might be causing the discoloring of the trunk.  I couldn't positively find a disease or fungus that matched what your tree 'damage' is.  Here is a link to help you find/hire an arborist to correctly diagnose what could be wrong.  If it is something like verticillium wilt, there are signs someone would need to verify in person.  Calling your local Extension office might also give you some local choices for an arborist.  https://ohioline.osu.edu/factsheet/hyg-1032